The series, set in Saitama, follows Ren Mihashi, who had previously excelled as his middle school baseball team's ace pitcher, due to his grandfather's connections as its manager. As he graduates to high school, whose baseball team his grandfather does not manage, he initially does not believe he is good enough to succeed at baseball, however, but assisted by his friends, he grows in stature, confidence and skill, helping his team excel with his own ability.

[Source: Anime News Network]

One year before the beginning of the story. Kaguyama feels intimidated by Haruna’s presence on the baseball team since he feels that his position as the ace pitcher is threatened. Kaguyama wants to quit, but Haruna talks him out of it after telling Kaguyama about his own past.

[Source: Wikipedia]

Ookiku Furikabutte recap OVA where the TV series has been reassembled into two 90 minute episodes.

Picking up where the original series left off, Ren Mihashi, the ace pitcher of the newly-formed Nishiura High School baseball team, and his teammates face the Sakitama High School team in the next round of the High School Baseball Invitational Tournament as they aim to play in the finals at legendary Hanshin Koushien Stadium.

[Source: Anime News Network]

According to HMV, the DVD & Blu-ray volume 7 of Ookiku Furikabutte ~Natsu no Taikai Hen~ will include an unaired episode 12.5. Director Mizushima posted in his blog that the special was made because they couldn't put the original manga episodes happened between the episode 12 and 13 within the TV series.