Give MC's death eyes more skill like special clairvoyance and mystic eyes skill through fate path.fans love evolving skill just look. Remember the fans reaction in naturo when more eye skill were introduced and saringan was evolved into mangekyo saringan.
Evolve sussano into ashura avatar there was Korean manga or manhwa or what ever they called soul cartel.in that Lucifer died and split into four part 4 devils born out the parts they were called archdevil.One of them is archdevil of slaughter Mephistopheles he cut of part of his own body(guy has high level regenerative power so they grew back) and made a giant ashura statue with it with 6 hands each of them carrying a blade he could summon each limb from a portal which opens in the sky which goes blood red when he open it and the hand destroy the opponent with his huge blade he calls it hells resentment and if need to go serious he summon the whole statue just check the manga out.Beside we already have real sussano in dxd world.
FBIultimate