Challenge/Request!
This is for any writer who's watched re:zero and pretty much any other show. What I'd like to see is a hero from another show joining the main cast, a role like reinhard, but more recurring. the character would help subaru and maybe be subaru's only confidant of return by death. the point is, we get another perspective to see subaru, experience another character's confusion and curiosity about return by death, and tie that character into the larger plot and maybe lore of the world. to restate, take an mc, or other character from a show, (naruto would actually be a perfect example of this, because he isn't too op generally and has a personality that could really fit in) and integrate that character into the supporting cast. as for the literary perspective, i'd recommend it to be from the introduced character and subaru, just extend the 3rd person perspective of the show with a focus on this new character.
ps. the integrated character himself can be from another world besides the one that subaru goes to, but please keep it a secret from the other characters until later on in the story. don't have an expositional thing early on where the new character tells everyone their entire backstory. you can have them from a different world, they just don't tell anybody early on...just like subaru.