Five words. Gateway of the Six Samurai
The reason why this card is OP is not because its limited.
It is because of the effect.
The effect states you can use ANY bushido counters on the field. This makes this card overpowered. Either use six samurai united to get counters, and use its gateway 4 counters effect and get shinai. Special summon. use gateway effect again. Keep doing this until you have 99999999999999 monsters.
So the lesson:
USE GATEWAY OF THE SIX SAMURAI
BEFORE IT DESTROYS YOU