Kemeko Deluxe!

Kemeko Deluxe! (ケメコデラックス! Kemeko Derakkusu!) is a Japanese manga series written and illustrated by manga author Masakazu Iwasaki. The manga began serialization in the monthly shōnen manga magazine Dengeki Comic Gao! on October 27, 2005, and is published by MediaWorks. The first episode of the anime adaptation was broadcast on October 4, 2008.

Plot
10 years before the events of the manga take place, 6-year old Sanpeita Kobayashi got engaged to his childhood friend, a mysterious pink-haired girl who promised they would meet again 10 years later, and she would become his bride. She then fed him a mysterious seed. 10 years after that day, Sanpeita has started to have dreams about his first love more and more. One day after the same dream, he wakes up to see robots crashing in to his room, who are then defeated by a small but powerful robotic girl. The girl identifies herself as "Kemeko" and tells him that from this day forth she is his bride. Remembering the girl from 10 years ago, Sanpeita at first doesn't believe that Kemeko is his first love, seeing as they look nothing alike. However, when it is revealed that Kemeko is in fact piloted by a pink-haired girl named M.M., who greatly resembles his first love, Sanpeita is thrown in to confusion as he tries to deduce M.M.'s real identity despite her claiming to not have ever met him before. M.M., in the guise of Kemeko, instills herself in to Sanpeita's life, moving in with him, becoming a teacher at his school, and likewise following him everywhere, presumably to protect him from the robots Mishima Electronics who are constantly targeting him for a mysterious power that he supposedly holds...

It is later revealed that M.M. stands for Mei Mishima, daughter of Souichiro Mishima, founder of Mishima Electronics. 10 years ago Mei, her father, and her twin sister Mai came to Earth in a spaceship. One day when her father was busy working Mei escaped from the spaceship to sightsee on Earth, only to get lost. Sanpeita and his friend, Izumi Makihara, then helped her get back home, and from there the three played together every day. One day, however, when Mei got lost inside the spaceship she discovered girls who looked exactly like her (and by extension her twin sister), asleep inside a row of test tubes. Mai then appeared, revealing that she had known about this and her father's projects, one of which included the "Nano Ball", a seed that when given time to germinate inside a host, was a source of limitless power. When their father arrives and warns them of the danger, Mai tells him that she has no intentions of stopping, and that she plans to use the power of the Nano Ball to create a perfect world for her and her sister. Mai then hands the Nano Ball to Mei despite their father's attempts to stop her, and Mei's memories, including all of her memories of playing with Sanpeita and Izumi, are obliterated by the power of the Nano Ball. Mai escapes, and their father, who has been mortally wounded by the Nano Ball, gives her Kemeko, and sends her off in to space, telling her to forgive Mai. Since then Mei lived as one with Kemeko, dedicating her life to protecting Sanpeita and the Nano Ball inside him. However, living with him is a constant reminder of what she lost, and she is devastated by not being able to recall any of the memories with Sanpeita that she kept in her journal.

In the last volume, Sanpeita is kidnapped by Mai, who has become the president of Mishima Electronics, and taken to Mishima. Mai reveals that it was she, pretending to be her sister, who fed Sanpeita the Nano Ball seed 10 years ago—now she is here to unleash the incubated energies of the Nano Ball. By kissing him she unleashes the Nano Ball on the world, which causes strange plants to grow from every piece of Mishima equipment around the world, with which she plans to destroy the world and create a new, perfect world for herself and populate it with children of the Nano Ball. Her plans are put to end when Mei destroys Mai's Himiko, an advanced version of the Kemeko, and kisses Sanpeita to seal the power of the Nano Ball. In the aftermath, Mei forgives Mai and decides to allow her to be put in an intergalactic prison instead of killing her. Mei tells Sanpeita that she has fallen in love with him again and the two get engaged, this time for real.