Summary (shortened to remove spoilers) by tethysdust from Mangahelpers via Manga Updates:

“Since their mother’s death, sisters Tomoe and Mikage have been mostly raising each other. The older sister, Tomoe, is determined to get good grades and work her way into a good college. However, she’s disturbed by the trouble Mikage sometimes gives her. The two sisters have their separate lives at their respective schools, but their life together and their relationship may be most important of all.”

The title translates to “Dream(s) seen by a fish”