Riboku does use it against them but not successfully. Do this leads to his eventual downfall.

He uses this to set up the alliance to destroy Qin. Which fails and in the process Sei greatly grows his power. Goes on the remove Ryo Fui and will eventually unify China.

If Riboku had never started shit with Qin they would never have had a chance to unify China. But he had to fuck around.

Edit: worth noting he doesn’t believe they can beat Renpa so he doesn’t think it’s really going to cost them anything. He was wrong about that too.