Neon's sword was givin to him by his parent, It, with out Thing's perrmission, at a very young age (10) the quirk is the gems, once someone he truly loves dies (this does not just mean romantic love) a part of their soul will go in one of the gems and gives him a new abbility. Like Osar, once Osar killed himself, a part of his soul went to one of the gems, and gave him the abbility to turn emimies to friends, and make them fight for him (forcfully, once they are put under the spell, they are not the same as before.) He took the sword with him, because he thought it would help him on his journy