Ken Ishiyama

Ken Ishiyama (石山堅) also known as Cementoss (セメントス) is a Pro hero and one of the staff at Yuuei. He teaches Modern Literature.

Appearance
Cementoss appears to be a humanoid block of cement. His body shape is evenly blocky all around his body. His eyes are generally closed and his lips are pulled upwards. His hero costume consists of a sleeveless black shirt with collar and black shorts along with a belt.

Personality
Cementoss can be serious when its necessary and can quickly change to a happy fan. Cementoss cares about the well-being and health of his students, trying to stop the match between Izuku and Shouto, noting that Izuku's injuries were serious and wanted to stop the match for Izuku's sake.

Unforeseen Simulation Joint Arc
At the end of the arc, he appears with alongside the other Pro Heroes. When Eijirou Kirishima runs over to see if All Might was ok, he uses his Quirk Cement to create a long cement wall to stop him from seeing All Might's true form.

Sports Festival Arc
Cementoss is seen creating the ring for the tournament event, which Present Mic thanks him for. After he creates the cement ring, Cementoss makes a cement chair for himself to sit on so he can act as the proctor for the tournament event.

During the fight between Izuku and Shouto, Cementoss contacts Midnight and asks her if he can stop their fight, saying that Izuku's injuries are serious and that even Recovery Girl won't be able to heal his injuries fully in a single session, noting that if Izuku was able to even win he wouldn't be able to fight properly in the next match. As Izuku and Shouto launch their final attack, Cementoss decides to intervene by creating cement pillars between Izuku and Shouto to try and stop them. However, Izuku's and Shouto's attacks hit Cementoss's cement pillars, destroying them and, as a result, creates a huge shock wave. After the shock wave subsides, Cementoss says that while the force of their attacks was not a good thing, he notes that the power was incredible.

Field Training Arc
In the faculty room, Cementoss informs All Might that a new nomination has arrived and the nomination is for Izuku.

End of Term Test Arc
On the day of Class 1-A's test exercise, Cementoss is one of the teachers that Class 1-A will face in their end of term test exercise. Cementoss will face Eijirou and Rikidou in their test exercise.

Rikidou, Eijirou and Cementoss arrive in an uninhabited city where their test exercise will take place. Cementoss explains the 30 minute test; Rikidou and Eijirou must either handcuff him or one of them must escape the battlefield within 30 minutes in order to win and pass the test. The test begins.

Eijirou and Rikidou keep smashing their way through Cementoss' cement walls, but the more walls they destroy, the more walls Cementoss keeps creating to keep them at bay. Cementoss tells Eijirou and Rikidou that their weakness is drawn out battles and advises the duo to push their strength to the limit. Eijirou and Rikidou are unable to get past Cementoss' walls by the time the End of Term Test finishes and as a result, they fail.

Quirk and Abilities
Cement: Cementoss's Quirk allows him to manipulate cement material that he touches,

Equipment and Weapons

 * High Density Weights (Combat Exam Arc) - Cementoss and the rest of the teacher used these bracelets to give themselves a handicap while they were fighting their students.

End of Term Test Arc

 * Eijirou Kirishima & Rikidou Satou vs. Cementoss: Won

All Might
He is a fan of All Might and was so happy when he met him for the first time.

Trivia

 * "Ken" (堅) means "stiff, firm, hard". "Ishiyama" (石山) means "Stone Mountain". "Cementoss" is possibly a combination of "cement" and "toss".
 * According to Volume 4:
 * He's a big fan of All Might.
 * He likes round things (whilst being, ironically, blocky).
 * His favorite food is manju.
 * On his profile in volume 4, the author commented that he should have given Ken's hair a crew cut.