When a gate to another world suddenly opens on Earth, Mikado City is invaded by strange creatures known as Neighbors, malicious beings impervious to traditional weaponry. In response to their arrival, an organization called the Border Defense Agency has been established to combat the Neighbor menace through special weapons called Triggers. Even though several years have passed after the gate first opened, Neighbors are still a threat and members of Border remain on guard to ensure the safety of the planet. Despite this delicate situation, members-in-training, such as Osamu Mikumo, are not permitted to use their Triggers outside of headquarters. But when the mysterious new student in his class is dragged into a forbidden area by bullies, they are attacked by Neighbors, and Osamu has no choice but to do what he believes is right. Much to his surprise, however, the transfer student Yuuma Kuga makes short work of the aliens, revealing that he is a humanoid Neighbor in disguise.

Sixteen-year-old Yuuki Hase finally finds the courage to speak to his crush and ask her if she wants to become friends. The object of his affection, Kaori Fujimiya, is a quiet and reserved girl who cuts herself off from everyone and does not spare him the same blunt rejection she gives everybody else. Some time after, Yuuki finds her eating lunch on the roof where she secludes herself during break. He decides to start meeting with Kaori every day in the hopes of beginning to understand her better. The more time they spend together, the more she begins to open up to him. However, nearing the end of the week, she starts to push him away once more. It is then revealed to him the reason for Kaori's cold front: at the end of the week, her memories of those close to her, excluding her family, are forgotten, as they are reset every Monday. The result of an accident in middle school, the once popular and kind Kaori is now unable to make friends in fear of hurting the people dear to her. Determined to become more than just one week friends, Yuuki asks her the exact same question each Monday: Would you like to be friends? Because he knows that deep down, Kaori wishes for that more than anything.

Beginning his first year of high school, all Matsuboshi Raidou wants is to make friends—starting with the cute, tiny, and soft-spoken Reina Aharen, who sits right next to him in class. Unbeknownst to Raidou, Reina shares the same sentiment, but she has a problem. Awkward and timid, Reina is incapable of determining how chummy she has to be when approaching a person. Due to Reina's complete inability to gauge personal space, the two struggle to spark their unlikely friendship, as even the simplest tasks like talking seem impossible for them. But despite the countless yet pointless challenges that hinder the pair, the overly imaginative Raidou will do whatever it takes to befriend the indecipherable Reina.

Hikaru Kusakabe is a normal, carefree boy in a rock band who is always focused on the present. During the summer, his entire class is forced to participate in an upcoming chorus festival. By coincidence, he discovers his classmate Rihito Sajou—known for being an honor student with excellent grades—practicing his singing alone. Sajou just cannot seem to get their class' song right, and Kusakabe, delighted at seeing a new side of his straight-laced classmate, offers to help him prepare for the event. Although their lives and personalities are total opposites, they begin to grow closer as time progresses. But with the pressure of an unknown future, what will become of them and their growing relationship?