Peko and Mahiru are classmates in Class 77-B, as well as participants of the Killing School Trip.
In the first trial, Peko gets embarrassed when everyone starts talking about the possibility of laxatives in her food, and Mahiru puts the boys in their place by disapprovingly scolding them and defending Peko's privacy. She is the only student who makes an attempt to defend Peko's dignity. Peko seems thankful for this, before the topic of the trial is finally changed.
However, during chapter two, Mahiru plays to the whim of the second motive: Twilight Syndrome Murder Case. Playing the video game supplied by Monokuma, Koizumi learns about the real-life murder that had occurred at their school. She chooses to address what had happened with everyone involved, despite them all having lost their memories of the case. Mahiru invites Ibuki, Mikan, Hiyoko and Fuyuhiko. However, the former two decline, having other plans.
Peko overhears Mahiru inviting Hiyoko to discuss the murder, choosing to send each a fake message and arrange Mahiru's murder. Mahiru confronts Fuyuhiko Kuzuryu (Peko's young master), angering the yakuza, who believes Mahiru to have a hand in the forgotten murder. Before Fuyuhiko could act, however, Peko bludgeons Mahiru with a metal bat. After urging her young master to escape, Peko rearranges Mahiru's body and left her in the beach house to be discovered by the other students later. Peko was later executed for her murder of Mahiru.
The two did not speak during Danganronpa 3: The End of Hope's Peak Academy.
- “And then, you looked at them with a kind smile... I couldn't help taking a picture.I like taking shots of people's smiles...and for a while, I couldn't get yours.”
- — Koizumi taking photos of Pekoyama in the Ultimate Talent Development Plan mode.
- “Yeah, your smile looks nice. Next time, I'll definitely snap a picture of you bursting out in laughter with everyone else.”
- — Koizumi to Pekoyama while looking at a photo of her smiling in the Ultimate Talent Development Plan mode.
- “As I said before, I exist as nothing more than a mere tool... I had no motive for killing Mahiru... No reason to kill...not even the will to kill... I was simply used as a tool. As long as I am a tool, I cannot defy my orders.”
- — Pekoyama in Chapter 2 of Danganronpa 2 talking about why she killed Koizumi.
Mahpeko is one of many ships were the individuals involved are victim and killer. Peko and Mahiru actually established a good relationship during the Killing School Trip aside from her becoming Fuyuhiko's "tool" in order to revenge Natsumi's death by killing Mahiru and Peko calls her murder of Mahiru "a senseless killing". In Peko's Free Time Events, she started to try to smile again after Mahiru told her that she is the only one who doesn't smile in her photos. Peko likes Mahiru's photo and said that she learned that her photos gave strength to people. Mahiru's defense of Peko during the first trial was where many members of the fandom entered the ship. Likewise, they see Mahiru and Peko's similar protective personalities as qualities that make them worth shipping. In the fan-game DRMK2 it shows Mahiru as the protag. She says that she wouldn't mind Peko protecting her.
- This is one of several ships between a victim and their killer, with the others being Leosaya, Chimondo, Yamaceles, Twoteru, Tsumionji, Band Aid, Nekodam, Komanami, Snatsumi, Nishichino, Amamatsu, Shiromami, Tojoshi, Shinnaga, Tenkiyo, Gokuiru, and Oumota.
- It is implied Peko had nothing against Mahiru and did it just to protect Fuyuhiko