Mikado Ryōko

Ryoko Mikado is the school doctor at Sainan High. She also helps out other extraterrestrials on Earth in various manners, usually those dealing with medical care, though she does offer students like Rito and his friends a variety of her own concoctions and some help concerning matters from space.

Appearance
Mikado has green eyes and brownish red hair, she also has pointy elf-like ears that she hides underneath her hair to blend in with other humans. Mikado often wears a lab coat, a pink top (that slightly shows the top of her breasts) that's held together by a belt on her waist and a black skirt. She has a slender and mature body that quite a few girls in the series envy her for. Her 3-sizes are B95-W58-H91. Or when she is not wearing clothes her underwear mostly consists of black lacy lingerie or in very dark blues and purples.

Personality
Mikado is kind to others, especially her students, including Rito and his friends, and would get mad at anyone who would hurt them (Chapter 79). She really enjoys teasing Rito's shyness around women.

She also shows that she is comfortable enough to converse with Rito in a serious and mature manner (yet still obviously caring since she was thinking of giving him advice even when nobody asked her to do so, albeit she never came up with anything in the end), as seen when she approaches him one on one inside his room to say that she likes the planet Earth and that Rito must do what he can to save it while enclosing his hand on both of hers seemingly comfortable in telling him her serious feelings and thoughts about the matter (episode 25).

It is also notable that she doesn't react shyly nor angrily when he was obviously having a perverted imagination during the middle of the conversation (a trait of Rito that characters of the series (one of which is Saruyama) notice whenever he's embarrassed or thinking of something ecchi), merely ignoring it even with his face visibly steaming red. Ryoko also has no problem with Rito seeing her almost naked with her clothes being melted by the king of Deviluke's plant traps or during their trip to the hot springs (where they shared a hot spring bath face to face with the inclusion of Saruyama). Furthermore, she seems to be smitten with Rito, shown when she once asked him to rub oil on her at the beach, and didn't look surprised when Rito accidentally says "I love you" to her, Nana, Yui, and Run. It also seems she is slightly perverted as seen in Chapter 36 of To Love-ru Darkness, after her garments are sucked off by Lala's machine Celine jumped up and began to suck on her breasts. She seemed to slightly enjoy it explaining that they always do it when they are bored.

History
Formerly an operative for a shadowy, black market extraterrestrial organization bent on overthrowing Emperor Gid, she fled from her superiors to Earth in hopes of hiding her identity. She now works as a doctor at Sainan High and runs her own clinic at her home where people and (secretly) aliens go to for medical help.

It is hinted that Mikado had met Yami prior to start of the series, which was comfirmed in Darkness chapter 38 when mention it being awful, Yami coming to her for treatment and full of injuries but with no memory of how she got them.

Powers and abilities
Though she has no unique special abilities, Mikado is a highly skilled doctor for both humans and many different species of aliens and an expert on a number of extraterrestrial matters. Although, in the anime, she is quite good at using her medical skills in combat, like when she went up against Pikari and wrapped him in bandages. She is very knowledgeable about herbs and medicines, and she may use them for varying purposes, sometimes even a little mischief.

She also has knowledge and access to various equipments of alien technology, including a regeneration tank much like the one used in Yami's creation and childhood, which she used to treat Yami's overuse of her powers. She was able to construct an artificial human body for the ghost Oshizu to use as her own physical body like a truly living girl.

Trivia

 * Judging by her pointy ears, it could be implied that Mikado is an elf, or a half-elf.