Looking for Japanese Movie but don't know title

I was once watching a Japanese movie about 5-6 years back and I was unable to finish because I was hurried to bed. The movie was on the Sundance channel so it probably an independant film, but nut sure.

I am 100% sure the film was in Japanese. Here is what I remember about the plot: There was a husband and wife and they didn't get along with each other very well for some point of the movie. They lived on an incredibly tiny houseboat in the middle of an ocean (lake, river, not sure). It wasn't really a houseboat, in the meaning it didn't like like a boat. It looked like a house could float.

I would really like to see this movie it was really good (if I remember some of the plot it must have been).

If you can help me that'd be REALLY great.

Thanks ahead of time.