I think the first Arc should be the same as it is presented as it is in No 8. Not exactly how Kafka's story goes but have the similar start. Then start cooking with the formation of the main Defense Force squad.
We should have character drama too like we don't all get along or something. We should also recognize that every player is important, and the characters need to work together in order to beat a Kaju. This is not like one character can solo.