Faputa claims to have known Reg before his memory loss. Their past relationship is, as of now, unknown, but currently Reg is unsure what to think of her.
During Reg's time in the orphanage, he and Kiyui are both Bell Whistles. They frequently spend time together when Nat and the others are out cave raiding. They appear to have bonded, as Reg makes sure to visit Kiyui and say goodbye to him before leaving with Riko for the Abyss.
Riko and Reg are the first people around Marulk's age to visit the Seeker Camp. He quickly bonded with them and they became friends. During their stay in the Seeker Camp he explained things about the Abyss and the Seeker Camp to them. When Riko and Reg advance to the next layer, Marulk, together with the other Bandits, sees them off. They share an emotional goodbye.
Nanachi first encounters Reg while he is trying and failing to save Riko's life after their encounter with the Orbed Piercer. At first, both Reg and Nanachi tend to be reluctant to show their feelings to each other, but over time they have become close friends and trusted comrades on their journey.
Nanachi doesn't like being touched by him, saying the way he does it is "too lewd". Reg often comments that Nanachi is fluffy.
Reg saved Riko from a Crimson Splitjaw in the Abyss's 1st layer. In return, Riko brought him back to Belchero Orphanage and, with the help of Nat and Shiggy, woke him up. At first, Riko was fascinated by Reg and saw him more as a Relic and advanced machine than a person. However, this did not stop them from quickly becoming close friends and learning to depend on one another's skills in the Abyss. Riko was also the one that gave Reg his name, and he treasures it very much because of that. Over the course of their adventures, Reg's actions and thoughts have shown that he cares deeply about Riko and feels very protective of her.