The level 1 characters catch up pretty fast, actually. I'm not exactly sure how exp is calculated in this game (it seems to differ slightly in battle as well, probably depending on the amount of damage each character dealt), but when I got Nitori, my party was level 7ish, and Nitori pretty much caught up by the time everyone was level 11. If you really intend on using the same 5 people over and over, let me remind you that the creators of this game liked splitting up your members into 2 or even 3 groups at a time. There's really no harm in grinding new characters when you get them, because it's really not that hard at all.
In terms of stats, they do sort of matter a lot. Especially the HP and MP, some characters are simply falling behind on them, and so their survival rate isn't very high. They don't even seem to have much of other stats to redeem said drawbacks, and so I left them in the roster as soon as I got some new characters. I do agree that what character you use makes little point, as Last Words don't activate incredibly often, and other than that they have no special qualities in battle.
In fact, there is a lot of advantage in using the same 5 characters over and over again. The more characters use their weapons in battle, the more they master them and learn new skills. I'm sure there's an upper limit somewhere, but my Youmu's got her 5th sword skill, which has a slayer effect against Angels and Demons, and with each skill she learns, the more bonus stats she gains from equipping a sword. I'm sure that given enough grinding, a single character could "master" all 4 weapon types in the game. 3, actually, because I don't think using a staff gives you any special skills to learn. However, the skills you learn and the stats that go with them only apply to the weapon type, so you can't just blend them all together, unfortunately. I have a sneaking suspicion though, that characters that are using weapons that are not their specialty will not be able to learn all of the skills that go with the weapon type. I'll have to do some testing to make sure.
The characters I left behind are
, and my current active party is
. I've cleared the entire top strata aside from the inside of the tower, and I have the following Shikigami:
Spoiler:
Komachi, Letty, Rumia, Wriggle, Minoriko, Mystia, Aya, Orin, Lunasa, Merlin, Lyrica, and that princess thing that you get from an event
. I'm wondering if there's anyone I'm missing.
I also found some sort of event item that looked like a glowing Suppository. I thought it would be an event for Reisen, but apparently not. Any idea what it does?