Was a bit concerned that every villain was going get "no longer allowed in another world"'d and that it'd get old. I'm glad this was not the case and I'm pleased that story acknowledges that some villains are irredeemable.
I realise that's the point but I want to highlight it anyway. This isn't yet another formulaic isekai. The story doesn't revolve around Sensei. I love how the solution to all otherworlders isn't to write a story and then banish them, but rather an actually compelling narrative conclusion. Suzuki returned to Earth after growing as a person, but nothing would change if Kaibara went back since he's long past the point of redemption.
When I heard his backstory I was thinking "ugh, is this the explanation?" but I also had a feeling that Sensei would never accept such a story, so I was thrilled when he straight up called Kaibara boring! Naturally, all the pieces fell into place when I saw him hand Tama the glowing book and any remaining doubts I had about this anime were erased.
I'm glad that Tama didn't leave the party, it would be damn boring without her. (And Sensei's disdain towards Nir's coffin-pulling skills was funny.) The mark of the divine beast felt a bit like a deus ex machina but it worked well in the end.