She is one of the main characters in the anime/manga series Love Hina.
Mutsumi was at Hinata Inn when she was 5 years old while her mother worked at the inn. Here, she would become playmates with Naru and Keitaro, and would be involved in talking the two into making a promise to make it into Tokyo University together. She would give up her Liddo-kun doll to Naru as part of the promise made. Her family would move down near Okinawa and would become the eldest sibling among seven children with the Otohime family. After graduating high school, Mutsumi winded up failing three times on her entrance exams to make it into Tokyo University. To take a break from the developments, she decided to go a retreat to Kagoshima.
Mutsumi was a major character created for Ken Akamatsu's Love Hina manga series. She was originally going to be made into a quiet girl archetypal character, but her character name later led her character to develop into the "weak and funny girl" utilized for the title's run. She has appeared in all anime adaptations of Love Hina which include the TV anime, Christmas special, Spring special and Love Hina Again OVA series. Mutsumi was voiced by Satsuki Yukino in Japanese and Julie Ann Taylor in English.
Mutsumi stands at 162 centimeters (about '5'5") with her three sizes being 90 cm for bust, 56 cm for waist and 85 cm for hips. She has long brown hair going down her entire back that she normally has braided and brown eyes. She is 20 years old in her first appearance in the manga and 21 in her first appearance in the manga.
Mutsumi has a rather unique perspective on life that involves plenty of optimism, naivety and ridiculous insights. She is surprisingly bright despite her seemingly air-headed behavior and only fails her entrance exams because her air-headed thoughts and anemia cause her to either make simple mistakes or be unable to attend the exams. Due to her anemia, Mutsumi is prone to fainting spells and is physically frail. Yet despite her weak condition, Mutsumi's optimism leads her to take part in activities that she shouldn't be participating in. She is interested in eating watermelons and laying in kotatsu. In addition, she has the rather unique ability to be able to understand what turtles are saying.
Naru and Keitaro first came across Mutsumi during their trip to Kagoshima and all three would stick together for the remainder of the trip due to needing a break from failing their entrance exams. The close compatibility that Keitaro and Mutsumi have in terms of personality and interests did lead Naru to develop jealousy toward them before the end of the trip. Mutsumi would later move into an apartment building across from Hinata Inn where she would frequently study together with Naru and Keitaro for cram school and entrance exams.
Mutsumi would later move into Hinata Inn when her apartment building burned down. Her presence would cause some tension in Naru and Keitaro's relationship as Naru started to suspect Mutsumi might be Keitaro's promised girl and a misunderstanding triggered via Mutsumi's sleepwalking led Naru and the other inn residents to suspect that Mutsumi and Keitaro slept together. Things would be resolved when Haruka uncovered Mutsumi's blunder and Mutsumi having knowledge of her time at Hinata Inn to reveal that she wasn't Keitaro's promised girl.
Mutsumi would later pass her entrance exams to enroll into Tokyo University and continue to support Naru and Keitaro with coming to terms with their feelings for one another. At the end of the series, she and Mitsune would take over ownership of the Hinata Tea Shop after Haruka got married to Seta.
Events with Mutsumi in the anime play out mostly similar to how they were in the manga, with some differences. Mutsumi's apartment building never burned down and a shut down of the Hinata Inn for construction led Keitaro to temporarily take up residence in the inn. A misunderstanding that developed in Mutsumi's apartment led Naru to doubt the possibility of having a relationship with Keitaro before the other girls reassured her that Keitaro still cared for her. Mutsumi would reveal that she wasn't Keitaro's promised girl during the Christmas special in the anime.