Gastro

Gastro is one of three assassins that was hired by Akira Takaoka in Okinawa along with Smog and Grip. He loves the taste of a gun, so much that he uses it as a utensil.

Appearance
Appearance-wise, Gastro is one of the more flamboyant-looking characters in the series. He has dark, spiked-up hair and furrowed brows, and tends to wear classy clothing. Strangely, when his gun is in his mouth, his eyes tend to go unfocused and point in different directions.

Personality
Gastro is a professional hitman who takes pride in his skills. Although he is a capable professional, though, he has a sense of honor, and considers cruelly poisoning a class of middle schoolers beneath him. However, he has one particularly odd personality quirk: he considers the flavor of his gun to be exquisite, and is often seen with it jammed into his mouth (occasionally covered in soup).

Synopsis
Gastro first appears as an assassin to stop Nagisa and the others from retrieving the antidote from Takaoka.

When encountering part of the E-Class in the theater, he easily spots every single of their locations, shooting at them, though they luckily survive due to taking cover. Though the E-Class feels hopeless, Korosensei comes to the rescue and distracts Gastro with his unique, invincible form, while giving the remaining E-Class members directions to swap positions to confuse Gastro.

Though confused, Gastro finally believes to have located an E-Class student, waiting for their movement. As the "student" moves, it only turned out to be a decoy, made during the attack itself. Chiba and Hayumi work together to disarm Gastro, leaving him to be tied up by Nagisa.

After Takaoka is taken down by Nagisa, Gastro and the other assassins have actually escaped using their assassination knowledge. Though hired by Takaoka, they actually swapped the Takaoka's virus formula with a replica that only works for three hours, but doesn't end up killing the victims. He explains to the E-Class members that losing his reputation of being an excellent assassin would be better off than being worth a bounty for killing a class of students. He then leaves on a helicopter, explaining that he'll kill the E-Class only if they're worthy of it.

Abilities
He has the ability to know where his targets are and their precise movements, making him one of the best marksman to date.