As someone who is currently playing characters whose- not actually original characters, I feel compelled to put in my two cents about this
I am not that much of a creative person in making new characters, and if I do make actual original characters, it ends up simply being a self-insert of myself just put into Karakura. Furthermore, I just.. don't find that much enjoyment playing OCs. Nevertheless making one. It's just never been a thing, I think. I'm sure others will likely say that it is to be expected or its fine if it's a self-insert, but I have already made one such OC when I first started in SRP. I do not want a repeat
I find playing characters who I'm already familiar with in their personality, backstory and who I actually actively like to be a more enjoyable experience. But I do not simply just take characters from their universe and just plop it in SRP- it's not a multiverse rp server. There's- really a simple way to 'bypass' the rule of not playing already existing fictional characters into SRP- by not bringing their canon media's storyline into SRP.
Instead, you can change their last name, adjust their backstory to accommodate Karakura's more simple setting, maybe do a bit of fine-tuning of their personality to accommodate your roleplaying style. Probably say that your character's bright colored hair isn't actually natural and it's just dyed and leave it at that. And with a base like that, you can toss your not-actually fictional character into the Karakura world and let them develop naturally
I wouldn't really call this an 'Original Character', because in a way- it's not original. I did not think of the initial complexities of my characters' backstories or personalities- they had already existed, just adjusted to fit into Karakura's world. I would never have been able to think of this myself, so I never shy away from the fact that 'Yea, this character right here? Yea, it's exactly who you think it is' if there comes a day someone actually recognizes them from their existing canon appearance
In the case of the main characters I play in SRP, however, I can confidently say that they are different from their canon media counterparts. Canon Hiiro would not do the same things as SRP Hiiro as done, the same thing for my other character, Tatsumi. Why? Because even if their appearance, personalities and backstories are based on their canon media, the experiences they have gained and the relationships they formed are completely new- shaping their character into someone eventually different that makes sense in the context of Karakura's setting
That said, I will still give this suggestion a major -1 due to the lack of substance to the suggestion other than 'it'll be funny'