Stellarium

Kanata is a scientist. After his former love died he became a workaholic and alcoholic. He is working on an experiment when he accidentally makes a mistake and a boy suddenly appears. He tried to shake off the boy's existence by trying to dispose him because he is no human but his friend stopped him. Their relationship started to broad anew journey when Kanata gave him a name, but deep inside his heart Kanata feels an incredible pain caused by the reality that appear before him, a boy came from nothing whose resemblance with his former love is undeniable...

Note: Includes the one-shot "Shinkuu Teien (真空庭園, A Garden in the Void)" and one extra chapter.