Episode 3 of "Family By Choice" kicks off with an intriguing twist as the enigmatic billionaire, CEO Yang Dong-gu of Global Biz Partner, makes a surprise appearance at the school gates, confronting Hae-joon with the bombshell revelation that he is his father. Hae-joon is left reeling, stunned by the fact that Dong-gu is blissfully unaware of his existence, a secret that Seo-hyun had meticulously guarded.
Curiosity piqued, Hae-joon begins to probe for answers, but Dong-gu, caught off guard, hastily concocts an excuse and departs, leaving behind his hotel contact details, urging Hae-joon to meet him there for further discussion.
Elsewhere, Joo-won displays a casual indifference to the plethora of love letters left by her schoolmates for Hae-joon and San-ha. One girl confides in Joo-won, revealing that she doesn't mind if San-ha reads her heartfelt missives; her sole intention is to express her feelings freely. Meanwhile, Park Dal arrives with the report cards, prompting Joo-won to sneakily conceal hers after discovering she ranks a humble 23rd out of 25 students in her class.
Dal stumbles upon a letter hinting at Joo-won having a secret admirer, adding another layer of intrigue to the mix. As Joo-won heads home with San-ha, Dal finds herself at the basketball court, where she eavesdrops on a conversation between Hae-joon and Suk-hoon, uncovering the hidden truth about Hae-joon's biological father, deepening the emotional complexity of the narrative.
During the bus ride, San-ha's anger flared up over Joo-won's disappointing grades, reprimanding her harshly for her academic shortcomings. She drew attention to Hae-joon's similar struggles in academics, but San-ha quickly rationalized, asserting that Hae-joon's athletic achievements balanced out his poor grades.
That evening, Joo-won found herself scrubbing dishes at the bustling restaurant, sharing with Jung-jae the love letter she had recently received. With determination, she expressed her aspiration to work at the restaurant full-time in the future. Jung-jae, however, discouraged her, urging Joo-won to keep her options diverse and to ponder deeply about her long-term prospects.
Later that night, Jung-jae stumbled upon Hae-joon loitering outside the restaurant. Just then, Madam unexpectedly appeared on the scene, remarking that Hae-joon had increasingly begun to resemble Jung-jae after years of cohabitation. The conversation soon took a detour, and Jung-jae led Hae-joon back home.
After dinner, San-ha sought Hae-joon out on the rooftop, prompting him to open his heart about his inner turmoil. Hae-joon confessed his bewilderment over the sudden appearance of his alleged biological father. This revelation triggered a poignant memory in San-ha, reminding him of the day his mother abandoned him due to her aversion towards him.
Hae-joon apologized for bringing up a sensitive subject, but San-ha insisted that Hae-joon confirm Dong-gu's parenthood through a paternity test. San-ha's hypothesis that Dong-gu might be seeking his son for an organ transplant elicited a chuckle from Hae-joon.
The following day, Joo-won and Dal embarked on a mission to uncover the identity of the mysterious love letter's author. The duo trailed a group of boys but ultimately came up empty-handed. Joo-won then asked Dal to accompany her, boasting to Hae-joon about the letter's contents, only to be startled by the revelation that Hae-joon was absent from basketball practice.
Simultaneously, San-ha accompanies Hae-joon to Yi-hyun's office straight after school. There, Hae-joon inquires about Dong-gu's whereabouts from Yi-hyun and discovers that Dong-gu had deceived him. Yi-hyun becomes flustered while discussing Dong-gu, disclosing that he had stolen money from Seo-hyun when she was carrying Hae-joon. She further reveals that Dong-gu married a wealthy woman and abandoned Seo-hyun to raise Hae-joon alone.
San-ha is taken aback by Hae-joon's intense reaction and attempts to console him during their bus ride home. He then invites Hae-joon for a drink, where they delve into Dong-gu's return after such a long time. San-ha hands Hae-joon a card and suggests they indulge in a sweet drink to lift their spirits.
Joo-won feels excluded and upset with Hae-joon and San-ha for not including her. She is astounded when San-ha informs her that they are embarking on a trip without her.
The following morning, Dal arrives at Joo-won's house to spend the holiday with her friend. Joo-won confides in Dal that the boys had left without informing her, but despite Dal's presence, Joo-won decides to breach Hae-joon's privacy by showing Dal his disheveled room.
Elsewhere, San-ha and Hae-joon encounter Dong-gu at a luxurious hotel. Hae-joon demands to know why Dong-gu abandoned Seo-hyun when she was pregnant and wonders about his sudden reappearance.
Dong-gu finally confesses, revealing that, being without any children, his wife's family is excluding him from their vast wealth. He implores Hae-joon to join him in the USA to pursue a professional basketball career. Hae-joon is utterly disgusted and rises abruptly to leave.
San-ha and Hae-joon find themselves perched by the seashore, the latter throwing a tantrum about Dong-gu's perceived. San-ha intelligently points out that Aunt Yi-hyun ought not have concealed such pivotal information. Meanwhile, Dong-gu crosses paths with Jung-hae at his eatery, introducing himself as Hae-joon's estranged father. He procures a colossal amount of cash, offering it to Jung-jae as compensation for nurturing Hae-joon over the past decade. Dong-gu announces his intentions to whisk Hae-joon away to the United States, but Jung-jae steadfastly refuses the money, inciting Dong-gu's wrath.
Joo-won and Dal enter the scene, but Jung-jae asks them to take a stroll, where the duo encounters San-ha and Hae-joon. Joo-won persuades the boys to join them at the restaurant, but they decline. The girls soon realize that Dong-gu is the one engaging Jung-jae in conversation inside. The trio of kids, accompanied by Dal, hastily enter the restaurant but find Dong-gu already gone. San-ha volunteers to escort Joo-won home, allowing Jung-jae and Hae-joon some private time.
Jung-jae confides in Hae-joon that his biological father wishes to relocate him. He urges Hae-joon to remain and complete his high school education, his voice breaking with emotion during the conversation. Hae-joon, too, cannot hold back his tears, voicing his fear that Jung-jae might send him away. He recalls Jung-jae's solemn promise to care for him until his mother returns, revealing his deep-seated anxiety about being deserted. Jung-jae comforts Hae-joon as he weeps, while San-ha reveals the truth to Joo-won, painting a vivid picture of their intertwined destinies.
Joo-won gently proposes that Hae-joon could, on rare occasions, reconnect with his biological father, mirroring Joo-won's own encounters with his estranged aunt. Hae-joon's heart is warmed by Joo-won's earnest assurance that he doesn't want Hae-joon to ever part from their cherished family circle.
Meanwhile, Dong-gu retreats to his hotel room, where an unexpected encounter awaits him—Jung-hee, who has journeyed to the city with the aim of introducing her daughter to her elder sibling, San-ha.
As the night descends, Jung-jae and Dae-wook share a drink, hashing out strategies on how to navigate the delicate situation concerning Hae-joon. Up on the rooftop, Joo-won, with a hint of mischief, unfolds the tale of the clandestine love letter, waving it about with a flair that captures the attention of both Hae-joon and San-ha.
