Arthur- Suzaku's pet cat. Sebastian's actual friend on campus. Arthur visits him frequently and Sebastian loves to pamper him in excess. Kitty. <3
Makoto Kino- One of his better students in his Home Economics class. One of the few girls that thinks he's handsome but isn't afraid of the other girls picking up on that.
Buffy Summers- She's the Slayer. Of course he'd know who she was, even if she wasn't taking his class.
Aerith Gainsborough- She had a cat. Of course he was going to talk to her. He never actually caught her name, but he knows that the cat's name is Zeus.
Claire Bennet- In his class. She doesn't seem to like him much.
Peter Petrelli- He's killed Peter a few times. It was incentive for Peter to fix a problem he had created though, and it worked. Sebastian intimidates Peter quite a bit, but on Ciel's orders Sebastian is keeping a bit of an eye on him to make sure he doesn't interfere where he doesn't belong.
Alois Trancy- A child who has taken an interest in Ciel and Sebastian both. Sebastian is wary of his butler and has no intent of obliging Alois. Nor being nice, given who his butler is.
Claude Faustus- Another demon and Sebastian knows it. Claude's master is after his own and Sebastian doesn't appreciate that, nor does he have any intent to relinquish Ciel. These two are rather competitive with each other, depite being polite on the outside.
Eiji Kikumaru- The student council president, who happens to totally think Sebastian is fun to bother.
Kafuka Fuura- One of his students. He and Kafuka get along and she calls him "Professor Kitty."
Ciel Phantomhive- His master. Sebastian's law and eventual prize. Anything Ciel asks of him, Sebastian will accomplish.
Soma Asman Cadart- One of Ciel's "friends." Sebastian is well aware that Soma thinks he's intimidating. Occasionally, Sebastian will provide Soma with properly cooked curry, but Sebastian does wish that Agni were here to take care of the prince himself. (No, really. It would make things much easier and be far less annoying.)
Morrigan Aensland- She's the head honcho of Makai and a succubus. Sebastian doesn't necessarily like her but he's finding he doesn't really dislike her too much either, so long as she stays in line. He has orders from Ciel to speak with her regarding her eating habits.
Kadaj Espere- One of his students, they've had too much interaction to be considered only acquaintances. Sebastian thinks he's an annoyance, but has been told to watch him more than once. Now that he's no longer a threat to Ciel's mission, Sebastian holds very little interest in him.
Harumi Fujiyoshi- A peculiar girl that provide Ciel and Sebastian with information occasionally. He has not been given order to find out how she knows what she does, but as long as she stays in line he leaves her alone. She has no particular use to him other than an occasional shortcut to answers.