The two rarely get to 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 for help to prepare for the girls-only party. He agrees to help, although he's kicked out of the gathering as soon as he's finished helping. Mahiru is the first person Hajime faces during a Rebuttal Showdown segment in Class Trials.
In the only Special Time Event of Chapter 2, Hajime sneaks in and 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.
While it was never showed in the main storyline, but in her Free Time Events, it's implied that Mahiru has romantic feelings towards Hajime. When Mahiru took a candid photograph of him, Mahiru didn't want to delete it even though Hajime told her to delete it. After revealing that she likes the candid of him, Mahiru blushed and ran away, saying that she needs to go somewhere.
In her last Free Time Events, Mahiru asked Hajime to take picture of her so she can see how Hajime saw her. She said that she liked Hajime's shot as much as her mother pictures she did. Mahiru also added that she would give him her old camera.
In her Island Mode ending, in thanks for Hajime helping her find joy in her photography again, she will give him her old camera saying if he's going to be by her side then he'll need at least one camera too. Mahiru was highly implied about to confess her feelings to Hajime before she decided to stay silent, watching the ocean with both Hajime and Mahiru being silent. In the end, Hajime vowed to protect and escape together with Mahiru.
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 those fans who do. Its main ship rivals are Komahina, Hinanami, Hinamiki and Soapies, although some fans enjoy all of them.
- 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
- They stand next-to-next during the Class Trials in Super Danganronpa 2: Goodbye Despair.