In the media-based universe, Hiro Kamui is canonically the second game's protagonist.
Hiro is portrayed as the same exact way as Yuu Kannagi in both video game and manga adaptations.
- Yuno Ashihara - Starting off as friends, they eventually become involved in the plan to save the world from another Devouring Apocalypse; she commends them, realizing just how much Hiro and the remaining God Eaters go through just to keep others safe. She has hints of romantic feelings for Hiro, even when he complimented her songs as shown in Extra episodes.
- Ciel Alençon - Hiro becomes her first friend early on, and this is reinforced by him saving her, going against orders in the process. This display allows her to unlock her Power of Blood, and also teaches her the importance of bonds. Ciel goes on to create, and eventually perfect, the Blood Bullets with his help. She also becomes his Vice Captain after Julius' retirement. Even though they were friends, Ciel has romantic feelings for Hiro.
- Julius Visconti - He often trusts Hiro with crucial tasks, such as evacuating Nana when her Power of Blood goes out of control. He also has a tolerance for the questions Hiro pose to him, acting as a mentor on Gun-types and certain Blade-types. Julius, in the end, leaves Blood in Hiro's care before retiring, with the knowledge that he have come far as his vice-captain and can take charge from there. After rescuing Julius from Rachel's grasp and saved earth from the Devouring Apocalypse/Eternal Destruction; Julius asks for permission from Hiro to re-enlist in Blood, a request which he gladly accepts and they're now on friendly terms.
- Gilbert McLaine - Regards Hiro as a good friend, and after his Character Episodes are completed, his partner, though this doesn't stop him from berating Hiro for some of the reckless acts he commit. Hiro's direct involvement in the fight with the damaged Rufus Caligula allows him to awaken his Power of Blood, and bring closure to his failure to protect Kate Lawry.
- Nana Kozuki - One of Hiro's first acquaintances, and eventually, close friends. Nana's quirky ideas sometimes leads him to get hit with unfortunate consequences, such as an attempt at a new batch of rations causing him to get food poisoning, or a mishap with a Stun Grenade (mistaken for a Fireworks Grenade she and Licca crafted) knocking both of them out. Hiro's direct involvement in Nana's rescue allows her to fully control her Power of Blood.
- Romeo Leoni - Hiro's upperclassman in Blood, they generally get along well, although initially with Hiro's recent promotion to Vice-captain, he felt a bit jealous, but overcame that after talking to the Old Couple about how he feels about his teammates.
- Livie Collete - At first Livie is slightly distant towards Hiro. She even answered Hiro's question close-minded saying that she's fine when he's worried about her condition on her right arm. She does have a bit of a kind side after Hiro saved her from the cliff and apologized him for holding him back. After she knew that Hiro learned the truth about her past from Director Feldman, she finally opens up to him and his teammates, and she's willing to help them rescue Julius and end Rachel's plot. After the Spiral Tree incident has been resolved and Livie's officially transferred to the Blood unit, she and Hiro are on friendly terms at the end.
- Kota Fujiki - At first Hiro tries to be formal with Kota, but he prefers to talk casually. They get along very well, he also talks about the Outer Ghetto and why he keeps fighting. He and Hiro even talk about his teammates' personality quirks and he told Kota that both Emil and Erina get along very well even when they're bickering.
- Emil von Strasbourg - His flair for the dramatic often baffles Hiro in his Character Episodes, to the point of being overbearing. This also leads to Hiro punching him at his request -- potentially three times, depending on certain choices made.
- Erina der Vogelweid - At first, she has a one-sided hateful feeling of being inferior to Hiro because of her belief that Blood is a group of top-class elites, but eventually she changes her view after learning by how he fights in the field. As she realizes herself, they, in truth, aren't so different after all. Erina even goes as far as to call Hiro her 'senpai'. The gesture can be reciprocated with Hiro calling her their 'kouhai', as per one of the possible choices.
- Haruomi Makabe - Hiro shows rather obvious enthusiasm while dealing with him, showing a closet pervert tendency that only sticks out while around Haru.
- Kanon Daiba - Kanon first is introduced to Hiro by Haruomi and comes off as a just clumsy, slow-witted person at first until she shows her sadistic side in battle. In her Character Episodes, she is left by Haruomi to Hiro for combat training sessions as Haruomi feels unable to keep trying to teach her; this later leads into revelation that her Oracle Reserve was not unable to be used but rather locked by Licca as per Haruomi's order as her previous instructor. Her current instructor Hiro makes Kanon train and practice hard before letting her use Oracle Reserve. Kanon looks up to Hiro as her "instructor-teacher/instructor-sensei" (教官先生) and even introduces Hiro as such to her former Defense Team comrades.
- Lindow Amamiya - Lindow develops a keen interest in Blood Arts in his Character Episode, and during this time, he refers to Hiro as 'sensei'. He asks Hiro if he would like to join Cradle after the battle against the Kyuubi, an offer that is either refused in the ending of Lindow's Character Episodes as Hiro has the Blood unit to take care of, or left pending. In the same Character Episode, he also talks of his experiences in becoming a parent, and how people who stand by you even in the darkness eventually become irreplaceable comrades. The latter seems to be a reference to Ren, his personified God Arc.
- Soma Schicksal - Soma apologizes for not being there to help when Hiro and his friends set off to the FRIAR, though they do make up for that lost time by going on missions together. His Character Episodes involve the revealing of his history from the first game to Hiro and his understanding of the world since 'that person' (the first game's Protagonist) became part of their branch. This is most notable in "There Is More Than One Correct Answer" （”正解はひとつじゃない”）.
- Alisa Illinichina Amiella - Started off as comrades and friends.
- Tatsumi O'Mori
- Brendan Bardell
- Shun Ogawa
- Karel Schneider
- Gina Dickinson
- Licca Kusunoki - She approaches him for help with testing the Link Support Device, and amidst their work together, she comments that Hiro is a hard worker, impressed by the effort he put in. She ends up on relatively good terms with him at the end of her Character Episode, declaring that she's happy with her place as an engineer.
- Satsuki Takamine
- Hiro's character design is based off the artwork of the male protagonist of God Eater 2.
- Hiro was given a casual attire in a manga adaptation. However, this never appeared in the actual game, because another male protagonist with Eric's hairstyle receives more focus in the game's promotional material.
- Hiro uses 2 different shields; one is a Buckler, shown in the GE2RB Opening Movie and a Shield, as shown in the manga. Interestingly enough, one of GE2's official wallpapers shows Hiro using a Shield.