Smog

A middle-aged male assassin from Japan, Smog specializes in "poisoning" and employs a spray-type weapon to release his self-made toxins. Obsessed with practicality and refinement, he even established his own dedicated laboratory for creating poisons.

Under orders from his employer, Akira Takaoka, Smog infiltrated Fukuma Island disguised as a waiter and served poisoned tropical juice to the Class E students. However, when the students infiltrated the Fukuma Denjo Hotel, his scheme was uncovered by Yuzuki Fuwa. Smog attempted to subdue Tadaomi Karasuma with a paralysis gas, but Karasuma's superhuman constitution allowed him to withstand the attack and knock Smog down with a knee strike.

Shortly after Takaoka's defeat, Smog appeared before the students alongside Grip and Gastro. Considering future risks, he revealed that he had engineered a non-lethal virus based on improved food poisoning bacteria, and then provided the students with a nourishing supplement. Following these events, Smog, along with his two associates, was taken into custody by the Ministry of Defense for questioning about the Takaoka incident. Before being escorted away, he left behind his own message of encouragement for the students.

Smog later visited Kunugigaoka Junior High's school festival at the invitation of Korosensei, where he cheerfully commented that the food was delicious "even with poison added." He continues to reside in Japan and maintains an ongoing relationship with Manami Okuda.