Setsuna No Rakuen
Yuzuki has always had an unrequited love towards her childhood friend Junya, but one day Junya starts dating his classmate Kaori.
Yuzuki was shouldering the pain that she would never be able to express her feelings to Junya. A while back, she had noticed that Toshiki was looking at Kaori with such a sorrowful expression. In order to obtain the paradise that she desired for, she decided to become accomplices with Toshiki but…!?
(Source: Chibi Manga)
Note: Includes the extra story "Hatsutaiken"