User blog comment:The Koromo/Crossover Battles We'd Like to See but Will Never Happen Outside of Fanon/@comment-1618120-20130101053245/@comment-972068-20130101213135

It's not a true fight if you change the character's elements in any way. Plus beating a Soul Reaper depends on how high of spiritual pressure you have.

So technically, the only way a non-Bleach character can beat a Soul Reaper, the result is all up to the author of the fight. No one else.