This is an excellent way of building up heat for this next villain - not only establishing that he's responsible for the past few chapters' events, but showing off in this chapter that he's not a one-trick pony, he's the real deal.
We're clearly not doing the typical cliche of the villain using his mind control thingy and then he has nothing else going on if the hero breaks out of it and stabs him. Nonono, this man is actually going to be a problem if/when he probably tries his eyes on Ginko and she's not turned into a puppet.
Ginko is a noble person, in her own way. She is, in her own way, compassionate for the man she had to kill, and this of course makes Sangetsu feel less on edge about her (given that he realized she's killed a lot of people).
...I think we miiiight run into a scenario where this new villain might mind control either Sangetsu or Miko and then Ginko has to fight them AND the villain, though. That seems quite plausible.