Try lunatic match mode. Use Marisa and play against Aya. AI never takes any damage, you can't win.
example here: http://www.youtube.com/watch?v=A-yIiyJASA4
- 1cc'd Lunatic Story Mode with Marisa, got a lot of points from Aya
- died a lot of times against Siki (reached her with 6 lives iirc, ended with 3)
- game crashed as I tried to save the replay (score was over 150 million)
- I was about to post here, then I saw "Match Mode"
- went to Match Mode and then Aya proceeds to redefine the word micrododging into "micrododging before Aya" and "micrododing after Aya"
- manage to get her to the last health bar on the first round, then die, then fail apart on the second round:
http://www.mediafire.com/file/48zldp9b1th0wb6/PoFV_-_Lunatic_Match_Marisa_vs_Aya_-_2011-04-23.rar (Gensokyo Replay Uploader's not working for PoFV atm, gives me an SQL error)
- I watch the replay and then saw Aya micrododge within the confinement of two laser beams, and micrododge the volley of blue stars from Marisa's boss attack which was supposed to corner her at the bottom right.. and come to the conclusion that beating her isn't impossible, but is something kinda out of my control
(you need to corner her somehow, when she doesn't have bombs, and this largely depends on your lasers to limit her space)