Midnight blade is not OP per say, but there are very few options to counter the early game dominance of the "Root of Warrior" passive, as of now those options include, the wind mains 4th mystery skill, Mifunes Mystery and the water mains 4th mystery skill (ew! pls dont). Some of the main characters like the poor fire main are almost defenseless vs lightning mains presently. The solution as many suggested is to go for the long game or my personnal suggestion the "hyper chakra" teams.

These teams use chakra generating abilities or ninjas to "cheat" higher costing mysteries in the earlier turns. The team with Mabui, Tenten and Mei is a good example of that. Almost all main characters have an ability that can generate chakra and you c*e those to use those high cost mysteries. Using the wind mains passive to generate chakra on a combo chase lets you use Gaara the fifth kazekages mystery at the begining of turn 2!