As a young kid Takuma is identified as having a heart condition that needs attention. He becomes friends with his doctors being treated at the hospital. Mayu overhears her father saying that Takumas condition is serious enough that he almost certainly won't live beyond the age of 20. So at 8-years-old he also gets a promise to wed Mayu when they turn 20, takuma isn't conscious of this himself, however. Later in life, Takuma becomes aware that he wont be able to keep this claim and also he begins distancing himself assured of protecting her from Mayu.