to be able to sweep you need to finish that stage in the previous day with full HP otherwise it doesn't let you sweep try using a team with shields and kill everyone at the start of round 2 before they can do stuff . i used gaara , kankuro gnw , naruto 3* and WB asuma to do win first 9 rounds without losing hp and i can sweep them now. Winning stage 10-12 with full hp doesn't work but it does change your opponents for the next day. This post was last edited by Haru no Owari at 2017-1-5 16:57
I'm not entirely sure if strict full hp is required, maybe low enough damage such that you start the next fight with full hp will suffice(you are healed slightly between fights)
it's been way too long since I've manually fought the thing, thou I think I was mildly damaged at some point....