White & Black
In my opinion while the ending seems something nice, in reality it is pretty cruel. Kouki doesn't really get his wish - he gives up his wings for Eiji's life -, he only gets Eiji's reincarnation, as a human baby. And no matter what anyone says that's not really Eiji, it's a new person with a brand new start. So there is Kouki, not really a human, not really an angel -but still with an awfully long lifespan- having to watchover human "Eiji" and hoping that he will also maybe fall in love with him. Yes, I know they got together in the end, but there was no guarantee for that and someday "Eiji" will grow old and die. So Kouki will get to watch his beloved die twice, then spend his remaining days -however long may those be- alone. Essentially he is being punished for falling in love.
Warehouse
On ch72 Re read later on if there are new translations
X'Mas Heart
Yoru To Asa No Uta