Chaka starts off as a young black teenager sharing a room with his unpleasant older brother, and turning into a pretty girl...turning into a mutant...having to leave home and go to a Superhero School...and he's thrilled to death about every bit of it.
The headmistress, Dr. Elizabeth Carson, gives the welcome speech and immediately comes across as someone you'd better not cross. Then later on, at Halloween, we meet her other identity, Lady Astarte, and we find out she's really someone you shouldn't tick off.
Trevor James Goodkind is a Sheltered Aristocrat, heir to billions in a wealthy anti-mutant business family and being groomed to be one of the Goodkinds who takes over the reins of power. We first see him and his family at dinner, being waited on, having a staff of chefs, and Trevor is plotting about how, when he grows up, he's going to get his favorite chef to come with him when he moves out. The next morning, he manifests as a mutant and things rapidly go downhill from there, with a series of Break the Haughty scenes.
The first episode of The Guild is just a long string of these for each of the characters, first establishing Codex with her weblog:
Codex: So, it's uh Friday night, and...still jobless, yay. I haven't left the house in a week. My therapist, uh, broke up with me. Oh yeah, there's a, there's a Gnome Warlock in my living room, sleeping on my couch.
Mecha Sonic's first appearance in Super Mario Bros. Z involved him vaporizing a poor Goomba at point blank range to retrieve a Chaos Emerald. That's probably the nicest thing he's done in the series so far.
The Yellow trailer acts as Yang's. She walks casually into a Bad-Guy Bar, uses a Groin Attack to get information, laughingly flirts with the same guy she was attacking seconds before, then punches him in the face for no particular reason. She then fights off the guy, his mooks, and leaves, greeting Ruby outside the bar.
Ruby herself has one in the first episode, in which she reads a magazine with her hood up while listening to music as a robbery is taking place. When one of the Mooks approach her she throws him out a window, clicks off her music, and pulls out her scythe rifle, fighting them off and chasing after the leader. Once a Huntress intervenes she immediately squees and asks for her autograph.
Intentionally tactless in Senpai Club: "My name is Tsumiki Domen. I'm 15 years old. My birthday is February 14! Beef bowls are my favorite food, and my blood type is A!" All in the first few seconds of the series.