Kono Koi ga, Zaida to Shitemo

Synopsis

When Chise was 8 years old, she met a boy named Chihaya. After losing his parents, Chihaya was taken in by Chise's family. Chise and Chihaya are now unrelated siblings... But they are gradually drawn to each other. But a cruel fate awaits them... (Source: Ciao Comics, translated)