The Marsh House is a abandoned house from the film When Marnie was There, released after The Tale of the Princess Kaguya. Marnie was born there, and lived there for most of her childhood. The Doi family moved in around the time Anna was visiting. Sayaka is part of the Doi family, and the house has Sayaka's Bedroom.
Anna Sasaki first spots the Marsh House while she is exploring the town. As she approaches the marsh, she notices an abandoned home. Later Anna dreams about a blonde girl, who is actually Marnie, the girl who lives in the Marsh House. Later the Marsh House is renovated by a new family, the Doi family. A girl named Sayaka moves in, who discovers Marnie's Diary.