The author said they were writing melodramatic Mary Sue trash and that's pretty much exactly what it was... a ridiculous little popcorn novel. 

Arc 1: fantasy, elf king x elf commoner
Arc 2: modern era, adopted son x father
Arc 3: cultivation, master x disciple
Arc 4: Sci-fi, royalty x marshal

ML has two fragments in this one so he's both the exiled prince and the usurping emperor

Arc 5: interstellar, ABO