toshi loves yumi but yumi is too naive. yumi's onii san who runs away from home met with toshi and seduce him. toshi embraced sumi as yumi's replacement. but when yumi find out, toshi lies that he love sumi because he believe that yumi never feel that way towards him. sumi is just one night stand but those lies affects yumi for so long and he always believe that. he didn't know what to do, he even offered himself to toshi as sumi's replacement which angered toshi.
Mimurake no Musuko