July 1st, 2030. Manga editor Nishino Mizuho is having the worst 27th birthday ever. The manga she’s in charge of will be ending. However, when she sees a group of high school students having fun, she recalls her own adolescence. 10 years ago, during her second year of high school, Mizuho had four childhood friends who she grew up with in a residential neighborhood known as Koigahama Highlands…

Kizuki, who Mizuho saw as the crybaby little brother of the group, has lately been hitting on her. Since Mizuho believed her and Kizuki would be childhood friends forever, she is not sure how to approach this situation. He's on her mind to the point where she seems disoriented, and even says something that could potentially push Kizuki away.

Afraid of ruining their relationship, Mizuho tells herself not to fall for Kizuki. All the stress makes her ill, and her friends come to help.

After spending the day at the aquarium, Kizuki asks Mizuho to cheer for him at his swim meet.

As the fireworks are set off, Mizuho rushes to look for Kizuki. At the pool she runs into...?

Mizuho is reluctant to visit Kizuki's house for dinner while her dad is away.

Shugo's older brother, Togo, makes a surprise return to Koigahama Highlands.

Mizuho goes out with Shugo and Togo and strongly contemplates her feelings for Kizuki.

Shin steps up as the student council president to ensure the Ao High Festival can be held.

The group goes on a camping trip! Airu tells Shin to be more selfish and he follows his suggestion.

Mizuho starts becoming aware of Shin's intentions after he kissed her at the campsite.

Shin and Kizuki compete over Mizuho. Meanwhile she finds out the results of the Newcomers' Manga Competition.

The year is 2030. Mizuho hasn't heard from Kizuki in years. But at the fireworks festival, she bumps into...?

Mizuho reminisces the day her and Kizuki started dating. Shin approaches Mizuho with his feelings once more.

Airu takes a chance and confesses his feelings to Kizuki and his delinquent past is revealed.

Mizuho believes her relationship with her friends could fall apart due to her dating Kizuki. However...

The seniors graduate and celebrate their last day at the pool, leaving behind heartfelt messages.

After a fight breaks out with Syugo and Kizuki, the friend group reunites for the first time in years.

Kizuki finally brings to light an incident from the past that caused him to break things off with Mizuho.

Airu reminisces the times he had feelings for Kizuki. Syugo's family restaurant faces uncertainty.

Kizuki quits his job to pursue swimming. Meanwhile, Shin is out with a fever and Mizuho pays him a visit.

Syugo and Mizuho spend their day together in Enoshima. Will Syugo finally confess or end with regret?

Shin successfully performs surgery on Mizuho's dad. Can he finally prove to Mizuho that he can make her happy?

After Shin's proposal, Mizuho makes a decision and goes to the pool to have a heart to heart with Kizuki.