TBH i don't see the endgame of this manga but my thoughts are...
1. MC fights his former party
2. Former party accepts the new MC and befriended the demons
But if number 2 is the route then what's next?? Another Demon faction pops up that is hell-bent to exterminate humanity and MC with his...
You wanna see the other kitty?
Yes!
Come with me, it's in this room
Where's the kitty?
locks the door
whisper to the ear Meow~
SEEEEEEEEEEEEEEEEEEGGGSSSSS