[@NekoMizu]
I had a bit of a mixed thing with the battle system.  It was unusual for an RPG so I liked it for helping make it stand out.  But I never played any bullet hells before so I tended to get hurt more often than not.  A few scrolling Shooters, a few dodge attacks... but no bullet hells.
...
Wait that's a lie.  I played a few levels of Bangai-O.  I don't think it really counts but it can get a bit hectic at times.
The hardest fight I ever had was... um, aside from trying to dodge all of Photoshop Flowey's attacks, was Genocide Undyne.  It's the second form of spinning-thrusting spears.  They get me every time.  I lost count how many times I died to her and her alone but it was around 94, 96?