As far as we know, TachiyomiSY has the same relationship with Mihon as it did with Tachiyomi previously. Maybe it'll change since SY's dev is also said to work on Mihon, but we'll see.
At the moment Mihon is the same as Tachiyomi with changed branding.
Kakao (hopefully) won't get to know the real names of the developers, which will prevent them from suing the devs personally.
They could try to DMCA claim the repo, but Tachiyomi is completely legal, so hopefully Github won't take it down. Github previously helped youtube-dl after they got DMCA notices.