The two rarely interact in canon, as a result of Mahiru's early death. However, they still share a fair amount of interactions.
Mahiru has high expectations for Hajime, much like any other male, which is why she acts rather harshly towards him during her introduction. In the second Special Time Event of Chapter 1, Mahiru asks Hajime to help prepare for the girls-only party. He agrees to help, although he's kicked out of the gathering as soon as the others decide he's done helping.
In the only Special Time Event of Chapter 2, Hajime peeks at Mahiru and Hiyoko taking a shower together. Later in the chapter, Mahiru asks Hajime to feed a tied-up Nagito Komaeda for her, which he reluctantly agrees to do.
Though it was never shown in the main storyline, in her Free Time Events, it is implied that Mahiru has romantic feelings towards Hajime. When Mahiru took a candid photograph of him, she didn't want to delete it despite Hajime telling her to. After revealing that she likes the candid of him, Mahiru blushed and ran away, saying that she needed to go somewhere.
In her last Free Time Event, Mahiru asked Hajime to take a picture of her so she could see how Hajime saw her. She said that she liked Hajime's shot as much as her mother's pictures. She even told him that she would give him her old camera.
In her Island Mode ending, she thanks for Hajime helping her find joy in photography again, and says that she will give him her old camera, because he needs one if he wants to be by her side. She was planning on confessing her feelings to Hajime in that moment, but she decided to stay silent, watching the ocean. In the end, Hajime vowed to protect Mahiru and escape with her.
The ship sailed as a result of Mahiru's crush on Hajime, shown only through their Free Time Events and Island Mode. In the main plot, there was no sign of her crush, though. As a result, not everyone is aware of the ship, although it's well-received among fans who do. Its main rival ships are Komahina, Hinanami, Hinamiki and Soapies.
- Hajime Hinata/Mahiru Koizumi tag on AO3
- Hajime Hinata & Mahiru Koizumi tag on AO3
- Koizume/Hinata tag on FanFiction.Net
- Mahiru/Hajime tag on FanFiction.Net
- Hajime's relationship with Mahiru on Danganronpa Wiki
- Mahiru's relationship with Hajime on Danganronpa Wiki
- Their trial podiums are next to each other.
- Mahiru is the first person Hajime faces during a Rebuttal Showdown segment.