Adding onto point-blank bombing stuff.
ReimuC is probably way easier to use for stuff like this, but her shot is not so good for inexperienced players. MarisaB is quite alright, despite the intimidating number of option arrangements she has. Blue tears stages apart and can shotgun, Red is straightforward. Basically, I know jack squat about the game or the shottype but that's something you're likely going to sympathize with. No need to get complicated with all the different option types. The others have their uses here and there, but they're not even close to necessary for a clear.
When using MarisaB however, you should autobomb any spellcard or nonspell you have abysmal capture rate on, no exceptions. If you really want to clear and do it quickly, that's the right thing to do. Try to get as close to the enemy hitbox as possible before bombing, because the center of the bomb (where the 5 colored rings overlap) does the most damage--enough to oneshot spellcards early on. Getting about 3/5 is ok too if you want to play it safe, though it's obviously most effective to ram into the enemy and deathbomb. Even after running out of bombs, it's not too difficult to finish off whatever spellcard you were working on to get some power back most of the time. This lets you bomb the next difficult spellcard so that you won't lose any lives in the process. The only thing to be aware of is how low you will be on power most of the time in the later stages. Just learn how to handle that and recover power when you can, and it's a winning formula.
Here's some Stage 6 replay with MarisaB for "autobombing" in a nutshell. Unless you absolutely suck at the last spellcard, this kind of route should be capable of clearing even if you enter stage 6 with no additional lives. You'll gain a life during the fight, probably die on the penultimate, get full power, bomb it a third or fourth time, then go into the last spellcard with max power for less trouble than what is shown on the replay. To summarize the replay, her nons are more or less static, and most things die in two bombs, except the penultimate (Hell's Tokamak or whatever it's called on Normal). Stage is a joke when entering at full power. It should be easy to copy if necessary.