Yokoyama Reina first joined Up Front Works label and Hello! Project agency as a Hello Pro Kenshuusei trainee member on August 17, 2016 forming the 26th generation following her failure of the third round for "Morning Musume。'16 Shinseiki Audition". On mid-November which follows, Morning Musume。'16 leader Fukumura Mizuki announces to Reina she's chosen as a Morning Musume。'16 member to fill up the 13th generation, only 3 months after her joining Kenshuusei. She's publicly announced on December 16, 2016 on Nippon Budokan stage during the last concert from fall tour "Morning Musume。'16 Concert Tour Aki ~MY VISION~", as an official member of 13th generation alongside Kaga Kaede. Inheriting from the official color golden yellow, she describes herself as a real spring rolls lover and someone who bet on her pretty smile to being loved. Fans of both japanese and overseas fandom will quickly compared her to Tanaka Reina and Kamei Eri, both legendary members from Morning Musume。6th generation, respectively thanks to her first name and her good looking similar to her. Tsunku♂ himself called her "Nidaime Reina" (2代目れいな) in lyrics of "Joshi Kashimashi Monogatari (Morning Musume。'17 Ver.)" (女子かしまし物語 (モーニング娘。'17 Ver.)) which means the second Reina, still referring to Tanaka Reina. At first, Reina will be strongly intimidated by her generation mate Kaga Kaede, mostly by her experience in Hello Pro Kenshuusei far superior to hers, but also because they don't find any common point. Therefore together, they will find a common goal: making Morning Musume。13th generation a legendary generation whose everyone will remember. 13th generation will be awarded Kudo Haruka as their mentor to help them integrate into the group and organize themselves in their work during one year, until Kudo Haruka gets her sotsugyo from Morning Musume。and Hello! Project as well. Three of them will held the 13th generation fanclub exclusif event on February 21, 2017 in which the new members will make their statement of commitment as Morning Musume。members, here's Reina's one :
"Statement of commitment, Yokoyama Reina. Thank you for welcoming me into the Morning Musume。thirteenth generation. I am now a Morning Musume。member and I will be forever. I was a Hello! Pro Kenshuusei member for four months. About my singing performances, I still have a lot to learn. But now I don't have to worry anymore. At first I was alone, but now Kaga Kaede is by my side and takes care of me. It makes me very happy. As a member of the thirteenth generation, I now contribute to a new formation of Morning Musume。. I hope to be able to discover all the possible learnings and succeed them one by one. I count on my senpai of course, but also on all of you to take care of me. From now on, I would do my best not to disappoint anyone. In the group, I hope to be able to hold a place similar to MC's because I like to speak, I also hope to be able to maintain very good performances at the height of the group. From now on, thank you for accepting me as a member."
Very quickly, the both new members will receive praise from everywhere, from the fans to the written press and even the members themselves. Many senpai at the time such as Iikubo Haruna and Ishida Ayumi praised their motivation and hard work, especially about their first choreography to learn (for their debut single "BRAND NEW MORNING") which is the most complicated the group has ever had since a long time. Some younger members was even jealous because they didn't recieved the same welcome when they had started a few years earlier. During one entire year, they will do works in collaboration, very motivated between their debut and the group 20th anniversary which was the same year. Thanks to many events organized to celebrate this important date, they could meet some legendary OG members such as Takahashi Ai, Michishige Sayumi, Tanaka Reina and even collaborate with the group first generation member on an official album and on stage as well.
In 2018, after this first year in the group, Reina will no longer work with projects in collaboration with her generation mate but rather works on her first solo projects such as her promotion into a regular MC place in "Young Town Doyoubi" weekly radio program, her first photobook "THIS IS REINA", media appearance in magazine or television program related to her favorite topics, ... Many of these projects will be rather positive, if we look at the sales of her first photobook which emerged from the first of sales. Reina also said herself that staff members and teachers will praise her many times for her hardwork - despite some personal problems at that time. It's also during this year that she will participate into some project related to a possible remake of the group Minimoni. such as unique performances to special events or photoshoots in some magazines. Finally, another group will be born "Minis。?", obviously based on the same main lines, but will be inactive quickly due to many activites from some of the members.
In 2019, Morning Musume。members will have many promotion activities related to the group releases but related to the Hello! Project 20th anniversary as well. They will held some solo events related to theses projects, such as ZDA events for the group 67th single, but it will be hard to add more activities since they also had annual concert tours. However, Reina will release a second photobook solo and have some promotions in magazines. This is still an important year in Reina's career since Morning Musume。will welcome new members to form the 15th generation. She's now a senpai and had some kohai to take care of. Later in the year, she will be promoted into the new generation's official mentor alongside her generation mate Kaga Kaede, after only two and half year career. It will be a heavy pressure for both of them but Kaede always have been a senpai in her kenshuusei time and Reina will take this opportunity to adopt a perhaps more mature role in the group. She came to talk to the leader Fukumura Mizuki about how she could managed them since she never did and it seems like Mizuki answers to her she had a full confidence to Reina about the right way to mentor kohai. On a more personal side, Reina will develop hobbies such as fashion and makeup. Through some Hello! Project original internet programs, she will be invited to present them and will even go as far as making tutorial videos. This influence will also be very present on her personal blog.
About 2020, it was a difficult year due to the mondial pandemic. Even if projects has been done on internet by the staff members, it was difficult for fans to see the group members elsewhere than on their social networks. This was the opportunity for Reina to benefit from a new instagram account which will quickly become popular. Activities exclusive to the 13th generation will come back and fans will enjoy photoshoots of them in several magazines. In addition to makeup and fashion, Reina will have a passion for hair colors and she's entering into a period where she changes it every week. Going through blue, pink, red, then blond, there will be huge success among the fans.