Worldbuilding Exchange v2

Donten ni Warau nominator here! Those are separate characters - a pair of twins that picked the same name for themselves. Isuke and Isame are semi-canonical in regards to their given names (the anime just inventedwhat they were), but they don't really use them. Fuuma I same would be the younger, and the older is listed as Kinjou Shirasu on ao3 as that's what he's introduced as initially to the audience. I just decided it's better to list them under the name they use, as it is the clearest way to have unambiguous character tags for both to anyone familiar with the fandom.