Eibriel

Be he foe or friend, be he foul or clea brood of Morgoth or bright Vala, Elda or Maia or Aftercomer, Man yet unborn upon Middle-earth, neither law, nor love, nor league of swords, dread nor danger, not Doom itself. shall defend him from Fēanor, and Fëanor’s kin, whoso hideth or hoardeth, or in hand taketh, finding keepeth or afar casteth a Silmaril. This swear we all: death we will deal him ere Day’s ending, woe unto world’s end! Our word hear thou, Eru Allfather! To the everlasting Darkness doom us if our deed faileth. On the holy mountain hear in witness and our vow remember, Manwë and Varda!

Maybe wasn’t that way before, but when signing up on Bluesky now you are asked to choose a instance (bsky.social being the default), and the username contains the instance name, exactly like any Fediverse account.