Kaette Kuru Ko

Hide's younger brother Yu died in a railroad crossing accident three years ago. His mother talks to Yu as if he were still alive. Hide can see Yu, so he thinks his mother can see Yu too. His mother's obsession with Yu gradually drives Hide into a corner...
(Source: Moto Hagio Works Library, translated)
Note: Published in English as a part of the A Drunken Dream and Other Stories manga anthology by Fantagraphics.