Fanart of Amatsuki. Source
Ama (雨) = Rain
Amatsuki is the deuteragonist and second playable character of Tsukumono Yume. You play as Amatsuki when you get Kozuki's ending. Amatsuki lives in a near-unfurnished room and refuses to leave for unknown reasons.
Amatsuki has long black hair that is tied back into a ponytail. His eyes are shadowed by his hair, so it is unknown what his eye colour is. Amatsuki wears a dark blue and gray kimono.
Very little is known about Amatsuki's personality, although some of the events you can witness playing as Amatsuki suggest that he experiences a lot of guilt.
|Spoiler warning: Plot or ending details follow.|
Not much is known about Amatsuki's past other than the fact that he is tied to Kozuki in some way, possibly being a friend of hers. Several events/effects you get involve meeting and/or interacting with Kozuki in some way (e.g. Bush Warbler and Disheveled Hair effects for Kozuki, Fox Mask and Bush Warbler effects for Amatsuki, Monochrome event for both, etc.)
The Monochrome events imply that Amatsuki tried to protect her from something awful, however Kozuki's ending may insinuate that he failed at doing so. Many of Amatsuki's endings imply that he feels extreme guilt over this.