Alternatively, if you're fighting 6PN who has lower BP, you can attempt to kill him within the first 2 rounds, which is possible with heavy dmg dealer like Shisui, Anbu Itachi, Fire main w/ buffs, Shin would be perfect here, but since you don't have him, maybe Iruka/AsumaWB/Bee.

Another viable strategy is full bt or at least chase and mystery bt Gakido as support, since his Y chase increases cd, which stops 6PN from being able to mystery every round.