"Those Who Move In The Dark" (暗躍する者たち, An'yaku suru Mono-tachi, Tonari: 119) is the 78th chapter of the One-Punch Man manga series.
While Speed-o'-Sound Sonic is training in the forest, he is attacked by two unknown assailants. They are revealed to be Gale Wind and Hellfire Flame, two upperclassmen from Sonic's ninja village. Gale Wind and Hellfire Flame ask Sonic to join the Monster Association and to kill Flashy Flash. Sonic initially refuses, but Gale Wind demonstrates his speed after transforming into his monster form. Sonic was surprised by their speed, accepted their offer, and took the Monster Cell wanting to give up his humanity to surpass Saitama.
At the Hero Association, the staff were discussing the sudden monster attack and their quick disappearance, with the exception of Marshall Gorilla who was still wandering the streets of W-City as he was not pleased with his disaster level. Rabbit, Meat Hammer and Hacker Net were sent to defeat Marshall Gorilla, but Zombieman offered to go instead. Zombieman followed the monster to gather information about the Monster Association, but the monster noticed someone walking down the street. Marshall Gorilla meets Armored Gorilla and was shocked to figure out that Armored Gorilla "sided" with the humans. Marshall Gorilla attacks him with his knife, only for it to break on Armored Gorilla, who proceeds to defeat him in one blow. Watching this altercation, Zombieman decided to follow Armored Gorilla instead.