For sandbox roleplays, I like using myself as the character, or some variant. This is one of those cases.
Name: Ken Dee
Age: 15
Gender: Male (let's go with that for now)
Species: Cyborg/born human
Appearance:
Personality: Extremely laid-back, Ken won't help unless he has to, but if things get too out of hand he'll reluctantly step up to keep everyone focused. He's intelligent and very logical, to a point where he'll point out all the flaws in something someone says jokingly or as a metaphor, watch them sweat and stutter, and then laugh at them. (...? Wait, this is me I'm talking about. |l<-<) It's hard to phase him, and usually he's fairly calm, but he jokes a lot too.
Bio: Ken was caught in a bad car accident on his bike when he was a kid and had to have his left arm and legs amputated. There was also severe scarring on his neck. He was already living alone, and had never known his parents, so he was put into an experimental program for integrating advanced technology into the human body. His limbs were replaced with machinery, along with part of his neck as a sort of interface. The antenna on his ear was just a bonus and all it does it pick up radio and cell phone signals. (...) There is a strong laser in his mechanical hand, put in as a self-defense tool to prevent others stealing the technology, and jets in his feet that he immediately requested after waking up from surgery and having things explained. He doesn't have very good control, but he's been practicing around the military base he's been living at since the surgery. He's had a few incidents with new staff calling him "unknown enemy aircraft", but the scientists have taken to introducing him to newbies.
As for the portal, he was accompanying the group of scientists who had overseen the operation to a science show, much against his wishes (in other words, he didn't want people poking him all week), when it appeared next to him in the parking lot as he was pulling his things out of the armored van they traveled around in, the others already having gone to check into their hotel room. So, conveniently, he has a decent amount of supplies when he goes through.