Umino Nagi was swapped with another child at birth. He’s going to meet his real parents today, but on his way to school, he meets a girl who is threatening to die to get out of her engagement.

Nagi and Erika are now engaged, but Nagi can’t wrap his head around how loaded Erika is, and Erika seems to have concerns of her own.

Living together with Erika gives Nagi an opportunity to focus on exam prep, except when they run into trouble.

Having scored higher than anyone else in his grade, including Hiro, Nagi decides to finally confess to her.

Hiro and Nagi begin studying together in the mornings, but unexpected circumstances put a wrench in their relationship.

Erika joins Nagi’s and Hiro’s morning study sessions to wingman for Nagi, and Hiro wants to come hang out at her place.

Nagi invites Hiro to join his group for a school field trip. The group is plunged into chaos with the addition of a couple more members.

Sachi notices something going on between Erika and Nagi and decides to try to get to the bottom of it. Both she and Nagi are on the verge of a big decision.

Hiro and Nagi go on date at the amusement park. Sachi is not amused.

Sachi and Nagi go shopping together for a Mother’s Day gift, but they can’t think of anything their mother would appreciate

Erika and Nagi are stuck in a power outage. Nagi goes to the front door to find an emergency kit, when the unthinkable happens.

Nagi tries to redeem himself after embarrassing himself in front of Hiro on their amusement park date.

Nagi is beginning to question his own feelings, and he has trouble even focusing on midterms.

Erika’s parents want her to come home if she fails her make-up exams. She asks Nagi for help, but it may not be that easy.

Erika and Nagi walk around the festival together, and she shocks him with how out-of-touch she is.

Sachi is worried about Hiro, so she brings Erika along to follow her and learn about her.

Erika, Hiro, Sachi and Nagi make plans to study at Erika’s vacation house, but there ends up being a slight change in the roster.

Nagi is hoping to do the test of courage with Hiro, but Erika takes him instead. Nagi can’t figure out what it is that’s bothering her.

Erika reveals who it is that she’s been trying to reach through social media.

Nagi discusses with Erika what he learned – or tried to learn – from her father.

Having topped his grade in the term exams, Nagi confesses to Hiro once again.

Erika, Hiro, Sachi, and Nagi spend more time at the beach home retreat, and eventually, clues about Erika's missing older brother are found. This incites Nagi to search for him around the nearby town with Erika by his side.

On the day Nagi, Erika, Sachi, and Hiro are to return home, Nagi and Hiro decide to stay behind to collect a shrine stamp from the local temple. However, become of this, their train ride home is canceled due to the stormy weather, thus forcing them to stay at a local inn where things get strangely intimate.

The household visits the diner to attend Yohei's birthday party and learn some family secrets surrounding them. The next day after a study session, Erika succumbs to a cold that she caught, and the household, including Hiro, scrambles to help her through it.

Hiro moves in with Nagi, Sachi and Erika. Friction arises, but they're reminded of what happiness might mean.

Hiro is kidnapped and Nagi immediately sets out to save her.

Nagi is suddenly hit with the truth about Ai’s real objective.

Hiro is preparing for a festival that's about to be held at her shrine.

The world now knows the face of singer Mochizuki Ai, who created the song “Arc Fault.”