I also felt Kai's monologue was kinda long, but I guess it makes sense he wouldn't just die in 5 seconds after getting pierced by an arrow. As readers we knew Kai was like, but now Sei also knows, and I guess that's why he is sad?? Because he understands he was a sad sack until the end? Also his first kill.
Thanks for putting up with this weird series for so long! It wasn't the best manga out there but I'm still grateful I got to read this.