Pirating_Ninja said:For Seinen/Josei romance I strongly recommend reading manga ... not as many are made in to anime however I feel that is more just a statement of good romances in general, most are manga... Also you want a happy ending which is common of Josei/Seinen romances too however ... if you want a more happy romance that isn't necessarily what you will find in Seinen/Josei since they are often times more realistic romances however having said all of that a few romance you might like include:
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Aishiteruze Baby (
Shoujo, this is more of a slice of life with romance becoming a more important part of the plot in the second half, the first half primarily deals with the male MC getting used to having to take care of his 5 year cousin who he has been forced to take care of after his grief stricken aunt abandoned her due to her husband's (his uncle's) death, it is a very heartwarming series and has a happy and conclusive ending romance wise (and no, the romantic interest is NOT his 5 year old cousin... this isn't that kind of show), a nice series but clearly not a shoujo/seinen although it isn't as cutesy and frilly as Kimi ni Todoke either)
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Clannad (
Shounen, my second favorite romance anime, the first season is very happy and very emotional in a happy way, the second season though ... is somewhat of an emotional roller coaster, however while this anime did make me tear up a bit I would like to state that this was NOT a tragedy and does have a nice ending, while this is a shounen (ignoring the art) this series, especially in the second series, is probably more mature in some aspects (do not mean sexual content) but emotionally is more realistic and less "all for one and one for all" like you find in most shounen series)
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Itazura na Kiss (
Shoujo, this series does give off a more shoujo vibe character wise however having said that this series does have a rather uncommon plot element that isn't too often seen, in fact the only other I can think of is the previous anime Clannad and another I will mention next, and that is this anime goes from meeting in highschool --> dating in highschool and college --> marriage --> kids and career (note has more than an episode dedicated to these, so its not like you see an older looking MC pick up a picture of his/her wedding day or of his/her kids and smile and that's it)
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Kareshi Kanojo no Jijou (depending on who you go by either
Shoujo or Seinen 0.o, anyways I myself have not seen it however this is a more mature toned anime that also has the whole dating --> marriage --> etc. element to it (done research and planning to read at some point, prefer manga in series where their aren't fight scenes since movement is not necessary and manga do a MUCH MUCH MUCH better job w/ romance), should be close to what you are looking for)
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Lamune (
Shounen, my 3rd favorite shounen romance anime, sort of a simplistic romance anime, very straightforward with mild levels of drama mixed in and actual romance, really enjoyed this short series because their was no element that bothered me, it wasn't amazing but imo it didn't do anything wrong)
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Lovely Complex (
Shoujo, read the manga so not positive but pretty sure the anime goes well past where they start going out too, the series is more of a romantic comedy if you are in the mood for that with drama mixed in since it is a shoujo, also while it is a shoujo the characters are extremely atypical for a shoujo series (not a shy girl and the guy is not perfect), rather liked the series)
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Nana (
Josei, haven't seen it but supposedly an amazing anime and ptw myself once I get back in to the romance phase... However not positive that it has a happy ending and the fact that you have avoided it might mean that it doesn't have a happy ending though haven't done too much research (in fact none) in to the ending of the series)
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Onegai Teacher (
Seinen, actually unsure if this is seinen or shounen however it contains sexual references (no nudity or sex scenes and is not an ecchi) and also features what is probably a very socially unacceptable relationship in Japan (well actually anywhere in the world) that honestly is extremely rare to find in anime/manga which is a female teacher x male student relationship being the main focus of the anime, I don't remember it being amazing however I did like it)
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Toradora! (
Shounen, My favorite romance anime, it was done extremely well and I really did like it, it would have been a good anime w/o the romance (although probably only 4 episodes w/o romance since they would have had to cut alot of the scenes) however of course with the romance it was just ... great!, I loved the characters which were pretty original as well as the general atmosphere (which is why I believe I could love it even if it was just a slice of life with no romance), it is not your average shounen and shouldn't be written off as such, a good romance anime)
Also as a side note, if you haven't already make sure to read
Nodame Cantabile: Opera Hen (a short 10 chapter sequel to the last season, link is to mangafox btw just as a heads up) ... Noticed it was one of your favorite anime and the ending to this short little sequel really is worth reading even if you don't like reading manga.
But yeah, I should note that everything I listed does have a conclusive ending and none of them are ecchi or harems (although Clannad might seem like it for awhile) ... And finally I believe that none of the ones I have recommended are too childish so if you are merely afraid of it being too childish don't worry too much about that.