Ikuta Erina (Morning Musume。9th generation)
Erina seems to have taken Reina under her wing very early on when Reina joined the group and repeatedly offered to go out with her. They have become close friends over time, always respecting their senpai-kohai relationship that Reina wishes to respect more than anything. Reina has shared an anecdote about Erina and herself: they very often confuse their respective outfits during concerts. Sometimes they have time to realize it and have time to exchange it, but there have been times when they have had to perform in each other's costume.
Haga Akane (Morning Musume。12th generation)
Akane and Reina have been good friends from the beginning but became very close around two years later. Their senpai-kohai relationship is more complicated taking into account their respective experiences and ages, but that's exactly what made it easier for Reina to go talk to Akane. Indeed, Akane being younger, Reina considers her primarily as a friend rather than a senpai. They have already taken a vacation together to one of Akane's family homes to go skiing, where Reina met her family. They have a lot in common and have a curiosity to learn and share their passions.
Kaede and Reina are generation mates and form the Morning Musume。13th generation, which is also the first generation of the group with only two members. Being both members of Hello Pro Kenshuusei, they got to know each other before debuting in the same group. Reina was very intimidated at first, especially during the Kenshuusei period, due to Kaede's experience which was far superior to her own. When they learned that they would debut together, they started to try to know each other a little more but were quickly discouraged by realizing that they had nothing in common; they were even their total opposite. Moving along at the same pace, they have managed to form a powerful, comical duo (defining them as a "manzai duo", Kaede being the tsukkomi and Reina the boke) and appreciated by the members and fans of the group. Today, Reina considers Kaede a friend, a senpai, a teammate, a rival. Their bond woven over the years has enabled them both to be mentors of the group's 15th generation, yet having barely three years of experience in the group. Being always very opposed on their respective personalities - even if they found common points - they managed to develop common goals: to make the 13th generation Morning Musume。a legendary generation that everyone will remember.
Morito Chisaki (Morning Musume。14th generation)
Chisaki and Reina became close as soon as Chisaki joined. It was considered as one of the cutest duo in the lineup at the time, bearing the pairing name "YokoChii" (よこちぃ). They talked to each other very often and respectively posted pictures of the two of them very often on their social networks. They also had a lot of work activities in common that make them spend a lot of time together, in addition to their personal outings. Reina considered Chisaki as her senpai, taking into account her experience in her former group, today she considers her as her pillar, multiplying the sincere declarations of love publicly in interviews, in concert, on her posts... The first time Reina did cut her haircut into a bob, she said it was also thanks to Chisaki because she wanted to have the same haircut than her.
Kawamura Ayano (ANGERME)
Ayano and Reina have joined the idol business world together, being part of the same generation of Hello Pro Kenshuusei. Being trainee together for just a few months, they managed to forge a very special bond of friendship that's still present today. Even though Reina started as a major very early on, she has always remained very close to her. Ayano admires Reina for her determination, her strength, her positivity, her talent. When she first saw her take the stage at Nakano Sun Plaza where she was making her major debut, she was more than astonished stating that she would never have been able to do what she had done. Reina considers Ayano as a big sister but they can even be considered best friends: they often go on personal outings together, they take advantage of any common professional activity to spend time together - such as birthday events where they invite each other - Reina even confessed that she would love to go abroad on vacation with Ayano, more specifically to Hawaii.
Nakayama Riko (Shiritsu Ebisu Chugaku)
Reina and Riko met at the ROCK IN JAPAN festival in 2018, when their two main groups were performing at that event. Reina was happy to be able to talk to her since she had been listening to the songs of the band for years already! Members (including Riko) came to see the concert at the Yoyogi of Morning Musume。'19. They have stayed in touch and posted pictures of themselves on their SNS.
Haruna Mai (Tacoyaki Rainbow)
Reina and Mai both attended an event in February 2019 and hit it off really well. Reina described Haruna as a very talented idol that she dreamed of meeting. In return, Mai also publicly posted that she was very happy to have gotten on so well with Reina and that she was glad to have become friends with her. A month later, when the show aired, Reina said that she watched the show with Mai over the phone and that they remembered this fond memory together.