From Blissful Sin:

Twins Keiji and Keiichi are both skilled in martials arts despite their innocent-looking faces. But the younger brother, Keiji, has harbored unrequited feelings for his older twin. What will happen to these feelings when Keiji suddenly enters a one-sided relationship with a schoolmate? What will happen when Keiichi also finds himself a lover?

A sexual omnibus full of trials and tribulations in these blue summer love stories.