that one can be done in like 5 seconds by using the piggy back method, although that makes the challenges go away and may reduce your enjoyment in getting the trophy
For those that don't know:
1 Equip appropriate titles on Cheria/Hubert/Sophie (e.g. Cheria's Alluring Temptress)
2 Make sure there is at least half accel bar full
3 Put on book of solitude, book of audacity, book of enthusiasm, etc etc, i.e. all books that halves stats, set difficult to chaos
4 Go up to boss, let boss hit you (for close to 999999), immediately activate accel to cancel dying animation, hit back, boss dies.
This can be done for any boss after getting the accel mode.