Mutsumi Otohime (乙姫 むつみ Otohime Mutsumi) A very sweet, very kind, scatter-brained girl who lives with her family on a small island off the coast near the main island of Okinawa west of its capital Naha. However, her family used to work at the Hinata House where, as children, she, Keitaro Urashima and Naru Narusegawa made a promise to one day attend Tokyo University together.
Mutsumi has her own unique approach to life; a combination of super optimism, naivety, and absurd insights. Despite her apparent air headed behavior she is, however, extremely bright and somewhat mischievous though this is hampered by her physical fragility. Prone to anemic fainting, her optimistic spirit is in stark contrast to her frail body. however, leading her to participate in various activities that would be unsafe for someone in her condition, But over time she gradually gets better to the point that in later parts of the manga signs of her anemia have left her.
Her mother working at the Hinata House, Mutsumi spent her time playing with Keitaro Urashima and, when her parents brought her to spend time at the apartments due to her illness, the pair included Naru Narusegawa in their games.
During one play session Mutsumi enacts a promise that all three of them would enter Tokyo University, further encouraging Naru to make the same promise again with Keitaro one year later, giving Naru her Liddo-kun doll. When her mother moved to an island near Okinawa, Mutsumi went with her; eventually becoming the eldest sister of seven other siblings.
Following graduating high school, Mutsumi began attempting the entrance exams for Tokyo University but, in spite of her intelligence, her air headedness and poor health frequently caused her to fail the exams.
Following her third failure, Mutsumi decided to take a trip of healing through Japan, and runs into Keitaro Urashima and Naru Narusegawa again while on a cruise to Kagoshima. Discovering that they, also, was on a trip of healing after having their Tokyo University entrance exams, the three travelled together for the remainder of her trip and saw her home to Okinawa.
During the trip Keitaro and Mutsumi exhibit uncanny similarities and discover many similar interests, so much so that Naru begins getting jealous over their compatibility.
Come the new scholastic year, Mutsumi made her way to Hinata to study for and attend the Tokyo University Entrance Exams only to become lost. Running into Naru and Keitaro again they discover that her apartments were across from the Hinata House and the trio begin their studies together anew. On the onset of the New Year, Mutsumi’s apartment is burned down, resulting in Mutsumi boarding and working at the Hinata Café. Keitaro becomes turn between which girl to pursue, and matters are complicated when Naru discovers that Mutsumi might be the promise girl Keitaro had pursuing these past years. Similar to how Keitaro performed when Seta arrived, Naru begins encouraging Keitaro and Mutsumi’s relationship in spite of Keitaro being undecided on who to choose.
While managing to pass his coming exams even while becoming freaked out and getting asked out on a date by Mutsumi, Keitaro’s confidence soars after it is cleared that Mutsumi’s Promise was made not to Keitaro but to Naru; clearing her of being Keitaro’s promise girl. However, he day dreams during the entrance exam and becomes convinced that, as he had rushed to complete it before the time ran out, he had failed the exam again. Not wishing to confront his friends and bare their disappointment he boards a boat heading overseas and falls overboard mid-voyage, ending up stranded on a tropical island called Pararakelse. Meeting Seta on the island, Keitaro volunteers to work as a hired hand in his excavations of the island.
Chasing after him, Naru joins Keitaro in the excavations; ending up getting lost in the island’s desert in search of the Turtle Civilization. When the rest of the Hinata residents, including Mutsumi, also pursue after them after learning that they had both passed their Tokyo University entrance exams Keitaro manages to send his entry ticket to the university on time to finally become a Tokyo U student.
On the first day of attending the university alongside Mutsumi, Keitaro suffers a broken leg when a roof ornament falls on him.
Following his return to the apartments he attempts to receive a response from Naru only to have her avoiding the subject in spite of Mitsune’s well-meaning meddling. When Motoko’s sister makes a proposition that Motoko either best her in combat or marry Keitaro; whom Motoko had lied about being her fiancé, and healing and witnessing Seta and Haruka’s own ponderous relationship, Naru finally reveals her conflicted feelings to Keitaro.
While travelling to Okinawa with Mutsumi to visit her family, Keitaro and Naru end up having to look after her when she loses her memory and regresses to her childhood, reliving the circumstances surrounding his childhood promise.
When Keitaro was drafted by Seta to help him in returning an artefact to the Kingdom of Molmol, the Hinata residents all pursue after them for varying reasons, resulting in a competition over who would have him between the girls, while Mutsumi follows along for fun and arrives at the Todai Ruins in time to ensure that Haruka's wedding gown makes it to her wedding.
Following the return to Hinata House, Haruka passes the cafe on to Kitsune and Mutsumi while she attends her honeymoon. Grandma Hina gives Keitaro the entitlement of ownership of the apartments, it is revealed that Naru was indeed the Promise Girl he had made his original promise to and the pair get married three years later.
Initially Mutsumi was designed as a quiet girl stereotype, however, after her name was developed she was given some foolish characteristics and became the "weak and funny girl".
Her model was inspired from a model in "Computer Lover's Dream".
She also resembles the Final Fantasy VII character Aerith,and even worn a dress similar to Aerith's.
In the Love Hina Character Popularity Poll, Mutsumi came in 4th with 284 votes out of 2506.
- In the anime, Mutsumi says “Ara” ("oh my") a lot. Her fixation with Watermelons and Kotatsu tables is also toned down greatly.
- Mutsumi has a habit of sleep walking, usually ending up in a completely different location from when she went to sleep.
- Mutsumi's height and BWH Measurements are 162cm, B90-W56-H85 as of Chapter 1 and 162cm, B94-W58-H88 as of Chapter 120.
- She is the eldest of eight siblings.
- According to Love Hina Mugendai, Mutsumi "died" 38 times throughout the manga's run.
- Kaolla and Sara once made an “Otohime Robot” as a statue to be erected in the hot springs, however it tripped and fell on Keitaro.
- Due to never having a boyfriend, and in an effort to save herself from embarrassment, Mutsumi used to make her own Valentine’s Day chocolates and pretended that they were for a valentine. Over the years she has become quite adept at making chocolates.
- She has the largest bust of all the female cast which is used for comical purposes many times.
- Some of the names Mutsumi wanted to give to Naru and Keitaro's children are Kei-ichi, Naruo, Narutaro, Keiko, Narumi, or Keina.
- Her surname and relationship with Tama and Keitaro may be a reference to the story Urashima Tarou where a man named Urashima Taro saves a turtle that turn out to be a princess named Otohime.
- Tokyopop sometimes misspells her name as "Mitsumi" or "Matsumi".
- Mutsumi is also the only one of the girls to never intentionally cause physical harm to Keitaro.
- Mutsumi's profile of her after the events of Love Hina from Love Hina Mugendai is as follows: