Nurse Angel Ririka SOS

Plot
Nurse Angel Ririka SOS (ナースエンジェルりりかＳＯＳ) is an anime series about a girl, Ririka Moriya, who is told she is the reincarnation of Nurse Angel, a legendary defender of the Earth from primordial times.

She is charged by Kanou, a visitor from the parallel world Queen Earth, with locating the Flower of Life, a plant said to be practically synonymous with Life, from which can be created the Green Vaccine, the bane of an evil force known as Dark Joker which has taken over Queen Earth and has now turned its attention to our own Earth.

The Flower of Life is supposed to exist in abundance on any planet where there is life, but on Earth it is mysteriously absent and is feared extinct, and Ririka spends almost the entire series alternately searching for it (following various false leads) and lamenting the impossibility of her task, all the while trying to fight off the attacks of Dark Joker with an ever-dwindling supply of Green Vaccine which is needed to cure those who become evil after being infected by the Black Vaccine. A plentiful supply of the Flower of Life is needed to create the massive amount of Green Vaccine needed to defeat Dark Joker. However the flower is a two-edged sword as it can also be used by Dark Joker to create the Black Vaccine.

Ririka is aided by her friend and neighbour Seiya Uzaki, and later by Dewey, a Bishōnen man who as an agent of Dark Joker had originally tried to kill her, but changed sides after she saved his life. (Dewey is arguably the most popular character amongst the largely female audience of the series.)

Ultimately Ririka learns that saving the Earth may require her to sacrifice her own life, when Queen Helena's psychic sister Princess Mimina divines that Ririka's fate is inextricably intertwined with that of the Flower of Life. Unlike in many heroic stories where characters seem to put their mission before their own life without hesitation, the prospect of having to give her life is profoundly shocking to this happy ten year old girl who had looked forward to a bright future, and who only embarked on her mission at all because of a rash desire to please Nozomu Kanou, the older boy she has a crush on and who turned out to be an emissary of Queen Earth (and consort of that world's ruler, Queen Helena).