As the person above me said, you can't get to so6p rank with the ninja you have.

The team I use to reach So6p rank is Earth main+Kushina BT+Edo Roshi BT+ Killer bee seven swords style, its very easy to get even for f2p players like me. 400 seal scrolls to draw edo roshi twice and gather the remaining frags for 4 stars from free events. He's in lots of events right now so it's easy to find his frags for a low price. Kushina Habanero is cheap in events too, save up frags from free events then buy the rest to get to 4 stars with coupons. I got her to 3 stars without needing to spend any coupons. And Killer Bee you can just get from survival trial points.