From Canis Major Scanlations:
Souji's life has been a series of dull events, with his parents endlessly quarreling, until he comes across Mika, a carefree student who lives each day as it comes.
They start a relationship which banishes heavy words like "love" or "devotion". They see each other occasionally, without making any promises and such.
But can an ordinary relationship make Souji say something like "I only got this far because you were with me?" As Mika says "Who knows..."