Yoshiko was the middle child of the Kominato's family. She is something that you might call the "glue" of the family since she's really the only one who can force her brothers to communicate with each other.
She's a genius at baseball, not necessarily a player, but the team who got her in their side would definitely got the upper hand. After an accident in middle school, she started her life over in Seido where she would meet a brother, 4 best friends and a cat.
[Only Yoshiko and the plot belongs to me. I certainly don't own Diamond no Ace or the Kominato's because if I do, God knows what will I do with them]