Marthy was a member of the Yakuza and a antagonist in Yandere High School
Marthy had blond hair that he hid under the Yakuza hat and his eyes were blue. He wore a dark blue suit along with a blue tie. He also wore a red kerchief in front of his mouth.
When Marthy first appeared he was shown as nice and ongoing, but when his true colors were shown he was revealed to be psychotic and aggressive as when Sam gave him money in return for his debt to the Yakuza. Marthy replied with "Burn it!!!" He then along with the other member began to violently corner Sam into various houses. Later on when being captured by Grian, PufferFish Pete, Sam, and Taurtis he was high on cocaine and seemed to have no idea he was even being arrested. The effects wore off and he responded politely with his community service sentence.
It is seen in yandere high school that Marthy would do anything for the yakuza and isn loyal to yuki and her father karu. He sees the yakuza as his family.
It is also seen that marthy has a interest in yuki from his body posture to her.