Uchi no Imouto no Baai

When Tatsuya was a child, his biological father abandoned him and his mother because she was always ill and had to stay in the hospital for a long time. Then she married to another patient at the hospital who was Yuuka's father. A few year later, they passed away and Tatsuya had to take care of Yuuka. They had been very close as children but when they grew older, their relationship gradually changed. Yuuka began to call Tatsuya "aniki" instead of "onii-chan" and she treated him coldly. Tatsuya even gave up his dream to become a professional baseball player to be always by her side before. Now what can he do to return to their "good" old days?

(Source: VNDB)