He is much more low-key than his teammates, and as such doesn't speak much, befitting his bored appearance. Despite this, he can be still be quite mischievous as shown when he held out his tongue towards the DA operator of the Tarantula mecha and waved it, and even grinning and yawning when he stopped the machine.

Like all members of Scavenger, he does his job of killing people and destroying things without remorse or guilt, willing to eliminate those who get in the way. Moreover, he also hates teachers and believes them to be the source of evil in the city.

Seike's ability is to control the coefficient of friction within a meter of himself, like Amime, though obviously in a much higher level. When setting the friction of air at maximum, even a 120-ton mecha is unable to move through the "wall." Apparently, any attempt to move through this wall where the coefficient of friction is at maximum converts the energy of that attempt to heat. As such, if a bullet tries to move through the wall, it will only heat up and melt. Indeed, Seike boasts that any material on earth will melt first before passing through the wall. Seike's ability can only be used for three minutes in a row.

He uses the first person pronoun "ore" to refer to himself, which is often used by boys, an indication of his true sex.

(Source: Toaru Majutsu no Index Wiki)