e: did someone say wall of text?
After spending several hours going through various scenarios, I finally somehow managed to scribble out from my head one that makes sense, in a way.
Leaving aside whether it was Alice or not, I'll just go ahead and try and deduce who was the killer from just the story.
As I mentioned before, there are more than a couple odd points throughout the story. I'll go ahead and list them below:
- Story02 is the only story with a specific narrator that doesn't end in a death
- Story03 is the only story where the narrator refers to their self as ボク (boku). In all the other stories, the narrators refers to themselves as 僕 (boku)
- Story03 is also the only story where a single character encounters the Pierrot and doesn't specifically mention how they died, if at all(?)
- Though the "Pierrot" is, up until story06, only mentioned right before the viewpoint narrator of the story gets killed, in story06 someone in the group says that they were captured by the Pierrot. In other words, this is the first time they 'encountered' the Pierrot without getting killed.
- Story06 is also strange in that there is a sudden change in location. Not a specific one, but the remaining 5 wake up in a dark place, having been captured by the Pierrot.
- Story09 brings up a strange occurrence of the narrator having been drugged with a certain '惚れ薬-Love Potion-'. The narrator falls in love with a "beautiful Pierrot" and dies in their sleep.
- Story10 is also strange, similar to story06, where the narrator seems to suddenly be transferred from their room to some place with a tree, where they are nailed to it to their death. Significantly, the narrator here (#3) has been suspecting one of the remaining two, #2 or #1, and sees their face right before his death.
- The narrator of the interlude prepares the breakfast of the next day during the night.
- The narrator (#2) realizes their breakfast was drugged and immediately regrets not killing the 'culprit' when they when mad, presumably #1, the only one left. They see a hallucination of the shrine maiden before they die, but see blonde hair instead of, presumably, the brown/black of Reimu.
- The last remaining of the honest men (#1) wakes up with a migraine with no recollection of the night before. He suspects narrator #4, who died from the love potion coffee, and hangs himself, being left all alone.
- In the postlude, Reimu remarks as having seen a pretty blonde girl heading towards the exit of paradise. This blonde girl, she notes, was the only girl among the 8 honest men.
So there are a lot of confusing points, but there are a couple that we can be assured of: there is one girl among the 8 honest men, and this one girl is the one that was left alive at the end somehow, and leaves Gensokyo. Also, we can be reasonably sure that story01 is true since there isn't much we can gain from it being false. So this much we know: that #8 was killed by the real Pierrot.
What do I mean by the 'real Pierrot'? The way the story makes the most sense to me is to realize that there are two killers in the story, the actual Pierrot who killed #8 in the beginning, and a second killer who later pretends to be the Pierrot. What led me to this conclusion were a couple consistent details. Firstly, all the deaths can be largely isolated into two categories: death by decapitation, and all other deaths. In all the stories were the Pierrot specifically was mentioned as the killer and the way of death was also specifically mentioned, it was described that the victim was beheaded by the Pierrot. In all the other stories, the Pierrot is not mentioned and the cause of death was something different.
That being the case, we can be sure that #8 --the curious one-- and #6 --the youngest one-- were killed by the real Pierrot, by decapitation. So what about #7? This is one of the biggest weird points of DiPP, and is contained within the stories 02 and 03. Story02 is narrated by #2, the early-riser, and only says that he was enthralled by the red-white shrine maiden dancing over the lake and comes to his senses when it started to rain. Story03 continues, or at least seems to continue, around where story02 left off. But this latter story is narrated by the beautiful one and is the only story where the narrator refers to themselves as ボク (
boku) instead of 僕 (boku). Considering that this narrator, #7, calls themselves the "most beautiful one", we can say with some confidence that this is probably the single girl out of the group. The different way of referring to herself, ボク, seems to reflect this.
However, I think this is a red herring. I think the use of ボク over 僕 indicates that
this is still the early-riser narrating. Despite having used ボク to seemingly refer to herself, the narration immediately continues to say that she would no longer be able to return to where "we" (僕ら--Note the return of 僕) are. There are a couple more conspicuous points that support this. First, story03 is the only story that seems to be a direct continuation of the previous story, story02 narrated by the early-riser. Second, though the Pierrot shows up, it is the only instance where a single individual encounters the Pierrot and does not get beheaded. Even more, it doesn't even mention how she died, only that she "was captured" by the Pierrot, who then disappeared into the storm.
With that said, let me say that this is probably the fake Pierrot narrating over #7's, the beautiful one's, place, faking their actions at the time. If you haven't guessed already, this means I'm suspecting #2, the early-riser, as the fake Pierrot, the one who started the narration the story before, story02. But with this comes up the question, why? Why would #2 murder #7, and go along murdering even more of his comrades afterwards? The answer I came up with is actually pretty simple, he was saving his own skin. With a kill-or-be-killed mentality. He must have witnessed a Pierrot-like silhouette enticing and then killing #8. Somehow, he manages to deduce that the killer must be within the circle of the 8 honest men. The figure must have been pretty feminine or something since he kills or drowns or whatever #7 first. To cover up his actions, he lies in his narration and then lies again in the next story-narration, narrating in the place of no longer present #7.
(Next is story05, narrated by #1, the cowardly one. He mentions that he no longer has any reason to live after his loved one disappeared. If we assume that he's referring to #7, then this would both seem to support that #7 is the lone female and that her disappearing somehow did actually happen. ie: that she's not in the group anymore.)
So when #6, the youngest one, is beheaded soon after, #7 panics. Didn't he kill the killer? He decides the drug the group or something and then relocates them somewhere further away, somewhere dark. This is story06. He is probably also the one in the group that mentions that they got captured by a "mysterious Pierrot". This description, "mysterious Pierrot", is the exactly same one used in the first story where #8 is killed, further supporting the idea that the early-riser must have caught a glimpse of the Pierrot somehow when they were killing #8, the first victim.
The early-riser's plan was probably to evoke some kind of reaction out of the rest of the group to see if he could determine the Pierrot. He probably didn't get quite what he wanted, but when they escaped save for one, #5 the wise one, and no one died for some time afterwards, he must have gone back and killed #5. To support this, #5 wasn't killed by being beheaded, but rather by being stabbed in the back or something. Shortly before #5 dies, he has an epiphany that 'the Pierrot' was among them, among the five that were captured. He probably deduced this when #5 mentioned they were captured by the Pierrot, or something similar. This is the second red herring of the story. "The Pierrot is within the remaining four!" is too obvious, not to mention it falls apart when approaching the last stories with this mentality.
To think about it rationally, why would someone in the group just arbitrarily bring up the detail that they were captured by the Pierrot? No one knows anything about any Pierrot since the only ones who witnessed such a figure all were decapitated immediately after (or disappeared, in the case of #7). Only #2, who caught a glimpse of the Pierrot and is actively trying to kill it and trying to evoke a reaction from the real Pierrot by pretending to be the Pierrot by claiming that they were captured by it, would be able to make such an offhand remark, which #5 deduces that he is the Pierrot from. If only half-correctly though, since he's not the 'real' one. To take his deduction at face-value, that the real Pierrot is in the group (and that there isn't a fake one) would greatly complicate things and lead to a lot of questionable inconsistencies and seemingly whimsical actions taken by a supposed 'infiltrated real Pierrot'. Only by having a fake Pierrot would things be consistent and sensible.
A short narration interlude indicates that the group had fallen to half their numbers. This is significant since it doesn't allow for there to be an uncounted 'liar' in the descending count of honest men. As in, like, there are 4 honest men left,
but one liar! kind of thing.
Story09 continues with the group after having escaped back into the building in the forest. There #4, the mature one, drinks his usual afternoon coffee, but it has been poisoned with the love potion. He "falls in love" with the Pierrot and dies in sleep. This is another strange point in the story. The love potion is also mentioned in the other DiPP story, where someone buys the love potion in secret from some shop. Since it causes the person who drank the potion is fall in love with the Pierrot, we can assume that it was the Pierrot who bought the potion and slipped it into #4's coffee. In other words, #4 was killed by the Pierrot.
The poisoned dead body is discovered by #3, the wary one, and he chooses to hide this fact from the remaining two. From this previous story on, we have an actual timeline of sorts. Let's call this the second-to-last day, and #4 has already been poisoned to death in the afternoon by drinking coffee. #3 discovers #4's body in the latter's room some time after in the day. Since #3 was the one to hand out the coffee to the others, he rules out suicide and immediately suspects one of the other remaining two as the culprit behind the murders. Shortly before he dies, he sees the face of his murderer and he sees the face of the one he suspected. This is a significant detail, since it means that either #1 or #2 was the one who probably killed #3. Since we determined that #2 is the fake Pierrot, we can expect that this is the face #3 saw before his death. How #2 managed to get #3 nailed to a tree from his room is one of the strange points, but if we ignore the curiosity for know and just acknowledge that his death was not by decapitation, we can be sure that it was at the very least not the real Pierrot. And hence, #2.
There is an interlude here. The narrator of the interlude is addressing someone, calling him too "spineless". This is probably the narrator addressing #1, the cowardly one. The interlude narrator then prepares breakfast for the next day during the night. There's a bit more, but let's move on for now.
The second to last story ends in #2's death. The early-riser realizes on the morning of the last day that the breakfast he just ate must have been drugged. He is dumbfounded that the truth managed to elude him until he and only #1 were left alive, and swears that he should have killed him back when the latter went mad. These last thoughts of #2 are where most of my thoughts of his motives for murder were. He says that it must have all been his, #1's, plan all along. He is likely thinking about #1 based on the 'back when he went mad' part, probably referring to when #1 turned into a youkai after trying to hang himself the first time and returned trying to pretend to be a human. But more than that, he was likely the first one to rise this, or even every, morning. Yet, he mentions that he and #1 are the only ones still alive.
How does he know that #3 and #4 are dead? The rooms were locked from the inside. #4 was poisoned in his room, and #3 chose to hide the fact before dying during the night. The only way he would know that only he and #1 are still alive is if he killed #3 after discovering #4's dead body. Since #2's motive for killing stems from self-preservation, he must have heavily suspected #3 for hiding the truth about #4's death and killed him later in the night. Hence, #2 knows that there are only him and one other left. Yet, here he is, having been drugged from his breakfast, and so his mind bends towards #1, now determined that it was #1 all along, that #1 must be the real Pierrot. Before he dies, he sees a vision of the shrine maiden from back in story02. Which makes sense, both this story and story02 are narrated by the "early-riser". However, this is a hallucination, this shrine maiden he's seeing has blonde hair. And who do we know has blonde hair? Why of course, the girl! #7, described by Reimu as both beautiful and having blonde hair, both descriptions that match #7. Significantly, the hallucinations both refers to stories 02 and 03, which is the ones that he lies about, bringing back attention to those. The Pierrot being described as "beautiful" also points to #7 being the Pierrot.
Lastly, #1 wakes up with a terrible migraine, having been assaulted by drowsiness after the last night's supper. He sees a poisoned body (#4), a body nailed to a tree (#3), and a
decapitated body. This can only be #2's body. Though the previous story doesn't mention it, this is the only one left. Since it was decapitated, we can determine that he was visited by the Pierrot before his death and decapitated. This is supported by the latter having hallucinated a blonde girl before his death, which we know is #7. #7 is the Pierrot, we've come this far and finally established that. Though in actuality it was a bit simpler than that. The killer must be the survivor, and Reimu sees the only survivor who is a girl. The girl is the survivor and is the killer, pretty simple, no?
#1 who doesn't know any of this suspects that #4 must have killed the other two and drugged himself to death. This makes sense. It would be difficult to nail yourself to a tree or decapitate yourself (especially if the head isn't around, though we don't know that). #1 doesn't know that #4 was the first to die of the last #4 in the building because #3 hid the fact from him. And so, having been left all alone, he hangs himself.
Now that all that is done, let's go back to the interlude. The narrator of the interlude addresses one of their comrades, calling them "spineless". If we assume that this is referring to #1, the cowardly one, then it supports the idea that this narrator, is the Pierrot and #7. Since the breakfast that the interlude narrator prepares is eaten by #2 the next morning, it can't possibly be #2, there's no reason to drug himself. Especially after going as far as killing to stay alive for so long. And seeing his boiling suspicions towards #1, the only other one left alive, when finding out that his food was drugged, we can be sure it wasn't #2. There is the possibly that it could be a split consciousness of #1 addressing himself, that makes things more complicated than simple and doesn't explain anything. Also, this is be only other mentioning of another of their comrades, if off-hand. The first would be #1's mentioning of the one he loved disappearing (#7). If this is #7 addressing #1, then this would complete the circle, not to mention the "spineless" description matches. Also, the description of track 11 UN Owen Was Her? says something along the lines of how easy it would be for a criminal with imagination to have a noose around someone's neck, like an activity before breakfast. And in actuality, #1 doesn't eat breakfast on the last day and hangs himself. Lo, a noose around the neck before breakfast. Thus, it wouldn't quite make sense for this narrator to be #1. Furthermore, the descriptions for the other tracks include the narrator buying the aforementioned love potion, and also uses the pronoun 私 (watashi--though, interestingly, before switching immediately to 僕 boku when beheading a doll, remarking that the rain seems to have stopped. Another reference to the events of stories 02 and 03, perhaps).
e: guess I forgot to mention that #1 becoming a youkai was also probably a red herring. The one who became a youkai immediately upon entering gensokyo is probably #7, which also explains how she survived #2 killing her or whatever he did to off her. The interlude, which I think is mistranslated in one part, suggests she wanted to return to being a thief, experiencing the wealth and activity of the city life. This matches up with how they were moving around as "honest men" for two years, which the prologue narrator describes as having been very boring.
tldr; the Pierrot is #7, the girl. To save his skin, #2 'kills' her and pretends to be the Pierrot to try and figure out who the real Pierrot is among the remaining members as the murders continue. He dies in the end, beheaded by #7, the real Pierrot.