Mitsuomi wasn't revived by Nagi
What leads you to believe this? If Nagi and the ones he brought back dies, that means big characters like Mitsoumi and Bunchinci or however you spell his name dies. Seeing as Mitsoumi has pretty much turned a new leaf, I find that unlikely.
Can't remember the exact chapter, it was something along the lines of "i'll become the strength for someone else", or something like that, and the subject of her thoughts was the approaching fight between nagi and masataka...
What chapter is this exactly? I recall her saying something about supporting Nagi, but I don't remember her saying anything about actually helping in any fight. Also, it looks to be a redo of Shin vs Mitsoumi, which was a 1on1, so it's very possible that she does not do anything but just stand there.