Yeah, that was me. I made it using animations, and while working on it, I ran into these problems:
1. Lots and lots of lag. Powerpoint wasn't made to have hundreds of bullets flying around.
2. I couldn't find a way to make the bullets appear, so all of them had to be put there before the spell started. This means that it's nearly impossible to make a full game in Powerpoint, because of the lag.
3. I couldn't find a way to have a playable character, so I had to make it mouse-controlled. This, ironically, makes the hitbox too big for any tight dodges - any difficulty above normal mode would be very literally impossible to dodge. The bullet hitboxes are also extremely large.
4. I could not give the boss a health bar, so it had to be a timeout spell.
I'm sure that with some more knowledge of Powerpoint, you could make bullets appear on command, or add a player character; but the lag will always be there. I also have no idea how one would go about adding enemies with health. It would take hundreds of slides; one for each enemy formation, nonspell, and spellcard. Recording scores would be a mess; there would be no replays, pausing, or shottypes; the list goes on.
Making a danmaku game in Powerpoint is possible, but not ideal in any way.