The opening theme is "Second Flight" by Kotoko and Hiromi Satou, and the ending theme is "Asu e no Namida" by Mami Kawada. One day while going to school, helps a young age at which a subject attempts to molest.
That afternoon, while working at home knocking on the door, turns out to be the same girl named Miina Miyafuji, she shows him a copy of the photo he has, saying he also saw the story and looking for his family, despite all Maiku is wary, especially because she wants to stay and live with him and not have a place to return, so it strives to appear as someone useful.
That night, again knocking at the door is a young woman named Karen Onodera, who tells the same story and shows their respective copy of the photo as well does not have a home, and ill health allows her to Maiku, and Miina stayed the night at home. Now Maiku, Miina and Karen should live together trying to discover who is the sister to Maiku and who not, and that little by little; they will awaken feelings against those who fight them before they can know the truth.
Onegai Twins opening theme "Second Flight" by Kotoko & Hiromi Sato
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Second Flight Lyrics
Kitto meguriawaseta Tenshi no hon no kimagure da yo
Sanpomichi de fuita suna kaze Kokoro ga hayatteku
Setunasa Hagurakasu no ni wa nareteru no ni
Konna toki dake namida ga tomerarenai no wa Naze darou?
Aimai na kisetsu dakara koso
Kasuka na tezawari Kokoro de kanjite
Kagirareta toki wo ikiru kara
Tatanda tsubasa wo ima sugu hirogete
Tatoe niji ga kowaretemo Sora wa matteiru
reference:
http://www.b-ch.com/contents/twins/index.html