To celebrate ryokugyu’s blade here’s a theory on how he might’ve got it
Crazy and out my ass but what if black blades are forged through a sacrifice. Like something crazy like killing a loved one or suicide. It being similar to zoan awakenings requiring death but still unique
We know Aramaki’s tattoo hints at suicide and death of a loved one. So maybe the sword originally belonged to a girl he really loved whether familial or romantic. Her death being what made the blade black with Aramaki deciding to hold it as a part of her. He can probably use it too but only when pushed to
Mihawk back in his youth definitely went through some big loss with it being tied to the betrayal he felt. Maybe after that lost he learned how black blades are permanently made and decided to try and achieve it. If he wasn’t strong enough he’d just kill himself but if he was he’d be able to overcome death and become one with yoru. If he didn’t try to kill himself what if the person that betrayed him used his own sword and literally stabbed him in the back leaving him to die. With the same effect either way. That maybe explaining his double ringed eyes because he and yoru are 1
There are a lot of ties between death and swords. Plus again the zoan comparison
This could also imply kuina is secretly alive sabo style since wado isn’t black. Which I wouldn’t mind tbh with her coming back as a man would be interesting imo
Ryuma potentially killing himself to make shusui black
It’d be mad funny if shusui did the same with zoro but he just didn’t realize because the blade is already black. Like if the scar on his eye is him deadass accidentally stabbing himself in the face lol. Him dying but surviving and growing stronger in the process. The blade wanting to be a part of zoro like it was ryuma. So it’d be like even tho he gave the sword up to wano it’s still with him in a way