 If you liked
Green Green
|
 ...then you might like
DNA²
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Both these anime series' main story is about a time-traveller from the future that is trying to change it from the past-line they travelled to. Basically Midori from Green Green and Karin from DNA2.
Green Green is pretty grotesque with its ecchi scenes, DNA2 isn't like that at all. Nevertheless, both have a bitter-sweet ending that leaves you at awe and are worth watching definitely.