Finally got Monstrous achievement. That was brutal, you need crazy reactions, to even play this game, but to survive for over 6 and a half minutes you need to be an actual ninja.
One big problem I have with this game is that the achievements are often not register, I had to get bakemono rank twice for it to register.
End of the Line achievement seems to be broken. No one have got it since 2017. The 3 people who have Monstrous achievement don't have End of the Line, despite you're pretty much guaranteed to get two consecutive runs, where you kill the emperor, while grinding for Monstrous. I got two consecutive emperor kills many times, even three consecutive emperor kills a couple of times, yet I still don't have this achievement. I think, it somehow broke after some update a couple months after game's release.