Exchange is back with its 4th season, and 8 participants gather at the house. They can only exchange their names and nothing else, but through the EX Introduction, they get to know more about each other. The bell rings after the meal, and an unexpected direction makes everyone confused.

The participants got to know about each other through the EX Introduction. It seems like the introduction made them curious about others, but then, the bell rings again, surprising everyone. The female participants must choose who they want to date the next day. After their dates are decided, the female participants get their chances to chat with their date’s ex.

The four couples go out on a date. Since the female participants chose their dates, all of them seem proactive during the date, and their chemistries make the hosts root for the new couples. However, when they come back home and meet others, the whole atmosphere becomes different. Meanwhile, Yoo-sik and Min-kyung’s story is revealed.

The eight participants are confused after having a date during the day. Some find new people charming, but some are bothered by their exes as they seem fine. Ji-hyeon expresses her feelings to Yoo-sik, and Min-kyung finds it uncomfortable. Meanwhile, a female catfish finally appears. Her moving in makes everyone nervous and confused again.

Baek-hyun’s ex is revealed, and their story is shared. With Hyeon-ji as a new addition, the tension in the air at the house changes. Baek-hyun has a hard time falling asleep with his ex added to the house, and he becomes emotional. The next day, Hyeon-ji reveals that she had a date with Yoo-sik to Min-kyung, and Min-kyung can’t help but have mixed emotions.

The participants go out on a date during the day, and everyone seems to like meeting new people. However, when the night comes, they all become emotional and feel confused. The participants are now allowed to reveal their occupations, and this new information brings some changes among them.

The Chatting Room is open again, and the female participants are invited. They wonder who invited them, and it turns out to be an unexpected twist. Meanwhile, the participants become more conscious about their exes as awkward situations keep occurring. Some participants want to be clear on their stance, and this makes their exes feel confused.

The new catfish, Jae-hyung, joins the house and meets everyone. The male residents feel somewhat threatened by his confidence. The next day, the Group Talking Room, where the male residents can ask questions to the female residents, opens.

The male residents must choose a keyword from the Group Talking Room. They will go on a date with different female residents according to the keywords they pick. At night, the exes get busy clearing misunderstandings and having deep conversations. Will these conversations change their minds?

The residents’ ages are revealed, and this changes how they feel about each other subtly. Once again, the drinking goes on late into the night, and some get angry about their exes’ behaviours. The next day, the Ex Room opens, stirring up their emotions once again.

The time has arrived again. With the Ex Room open today, some of them decide to check out the Ex Room, whereas the others enter the room because their Exes don’t choose to do so. Some feel more conflicted after seeing the room, while others hold on to their feelings. Where is everyone's heart going? Meanwhile, Yun-nyeong's ex will be revealed.

Shin Seung-yong, a new male participant, joins the show. His manly look and full package make the ladies’ hearts flutter, and other men alert. With a newcomer, some start opening their hearts. What changes will be brought into the house, and whose ex will he be? Meanwhile, all the participants are travelling to Kamakura, Japan.

On the night before travelling to Japan, some feel excited about the trip with their partner, whereas some feel conflicted and their relationships are strangely tangled. As the morning of their date in Japan comes, they forget the problems with their ex-partners and focus on their new partners, resulting in a smooth date. Will there be new love that blooms in Kamakura?

The trip in Japan continues. As they decided to let go of old feelings and travel with a fresh mindset, everyone's excitement doubled in Japan. Meanwhile, the exes will finally be revealed. Everyone will get to know who is whose ex and how they met and for how long they dated.

The doorbell rang again before the confusion died down. On the first day in Kamakura, a letter arrived. The men have to recommend a date for their exes. And starting from this episode, the receiver will get the sender's name when sending the message. Right now, when everyone knows each other's exes, who made your heart flutter?

Now that the exes are revealed, the atmosphere has changed. For some, it gets more comfortable as they can follow their hearts without hiding anything. For others, it gets more complicated as the relationships are tangled. The female participants choose the dates for the exes, and the result shows where they stand.

As their dates in Japan continue, some relationships deepen, and the direction of their hearts gradually becomes clearer. Those who hope to reunite with their exes show diverse reactions such as suggesting renewed promises and constantly trying to talk to them. Will these relationships move toward reconciliation? Or will they become more distant despite their efforts to win back their exes' hearts?

Hyun-ji and Yoo-sik go out on a casual date while everyone else stays home. Min-kyung talks to Yoo-sik after he gets back, hoping to hear that there’s still a chance for them to get back together. For the next date, the participants’ choices must be reciprocal for them to be able to go out. The result infuriates Min-kyung.

An envelope has arrived at the Kamakura House. The participants will play truth or dare for the final decision. One person can ask up to three questions. But they can't ask obvious questions regarding the final decision. Some honest answers stir up someone’s feelings in their final decisions.

Time is ticking until the final decision day. The participants go on a date with their ex with heavy hearts, thinking that might be their last date. After the date with their ex, each of them can choose one person, excluding their ex. If they choose each other, they will go on a secret date. Overwhelmed with uncontrollable emotions, their feelings become a tangled mess before the final decision.

After all the emotional ups and downs, they are finally reaching the end of the journey, and EXchange 4 is left with the final decision. Ex-lovers who broke up for their own reasons came together. New moments emerged from an unexpected encounter, and the new connection stirred up the time that had been paused with their exes. How will this season end?