This is what I use in 9tails/Group Summon. This is an Auto-friendly team with a very decent buff.

1. Main damage is Scarlet - specifically his Pure ninjutsu Chase. His standard is Tai/Nin which means not that 100% buffed compare to standard 3-4 (i think) but it is good enough to make sure chase is triggered each round.

2. Yamato Full BT give additional 50% damage all throughout the battle. His passive triggers when his Barrier is on is pretty useful too. He adds buff to himself and Rin. He can heal himself too with his passive.

3. Rin does pretty good damge too with her pure ninjutsu chase, even without her actual standard. She makes sure you survive Mysteries of summon, gives additional health as well.

5. Genma is for chase++ up to 5x max. Which means more damage from Sacrlet & Rin. His pure ninjutsu chase damage helps too.

6. Kotetsu's Ninja assist is very useful for scarlet, Rin & Genma.

This lineup is mainly for free users because ofc there are tons of other good ingot ninjas out there. hehehe

*** Better if you have MonkeyKing Summon Mystery i think for Scarlet Pure ninjutsu MS Spam every round haha

*** This lineup even in auto makes sure that no matter what happens scarlet will activate his passive buff first before actually triggering his chases every turn which is dope :)))

***The only downside of this (in auto) is when the barrier runs out and yamato has to activate it again. Yamato's MS is non-promt. Since the next round Rin will surely use MS, tho it will not trigger scarlet's, the barrier won't make it beore she executes her skills (MS&Chase). Anyways, if you really want 100% damage you can do it manually.

Overall i think this is a pretty good setup. Even low powered players i think can survive Gama/Katsuyu and grind 40cps, i hope so. hahaha

Hope this helps.