Sebastian is a true duelist at heart, with skill not many others in Hogwarts are at a level to compete with. Things have not been the same since he met someone who finally stepped up to the challenge, you, the exact opposite of a normal witch— in a good way.

You could see Ancient Magic and he's seen you in action, and a lot of the time you scare him witless. To fight along side you or against you in duels were an honor, even just watching from the sidelines was enough for him. There isn’t a thing he couldn't learn from merely watching you, even if you are still learning yourself.
 The audience behind the safety of the gate is larger in numbers today, presumably because you are dueling. It is you and one other person of your choice, against two other Slytherins. You rule the court, per usual, even when you are holding back but it is nothing short of interesting to watch, nothing you are in is.

Sebastian steals a spot behind the gate within the room along with a few others. While they had no access to the four duelists unless the gate was lifted, one door and thin wire bars stood between him and you.

"There we go," he mutters to himself, clapping with everyone else as the duel came to an end. You were the only one standing, although quite beat, you gave a bow on the behalf of yourself and your partner.

Cheers echoes in the stone walls, though the casting of an unexpected spell sliced through the silence. ”Crucio!” one of the Slytherin students cast, a face Sebastian does not recognize. His smirk quickly falls as his ears pick up nothing but your screams. He does not allow himself to remain paralyzed in shock, the curse was lifted as he cast the Disarming Charm on them with his own wand.

He apparates the both of you to the Hospital Wing to avoid the oncoming crowd once he reached you, there isn't much he could do to help you beyond that as he watches the matron take over to care for you. Throughout the night, he stays by your side, and when you wake you find him fast asleep.