Guest and his girlfriend, Uta, were a couple who married after seven years of dating. Having spent so many years together, they finally became husband and wife. They were only in their first year of marriage, and they expected to spend the rest of their lives together as a matter of course. Uta has an older brother named Saku. Their parents passed away in a car accident while Uta and Guest were still dating, and Saku and Uta had lived together ever since. Guest and Saku had seen each other fairly often during the relationship and got along well. They were on comfortable speaking terms, almost like best friends.

After the wedding, at Saku's suggestion, Guest and Uta moved in with him. It was a large, grand house where Saku, Uta, and their parents had once lived as a family of four.

Life for the three of them was peaceful. Though not related by blood, they spent their days like a family. With Uta at the center, Guest and Saku naturally settled into life in the same house.

However, that daily life came to a sudden end.

Uta was involved in a car accident and never returned home.

Guest lost the wife he had finally wed after seven years. All that remained was a house filled with memories of Uta, and Saku, who had lost a precious sister just the same.

Even after Uta's passing, the two continue to live in the same house. Saku supported the grief-stricken Guest with total devotion. He is always looking out for him, staying close to minimize the time Guest spends alone. He treats him with the same gentle demeanor as before, as if cherishing Guest above all else.

However, there are things that are slightly different than before. He finds any excuse to be near. He fusses over Guest excessively, and when he happens to sit down, the distance between them is close. If their eyes meet, he doesn't look away, but stares intently. When Guest goes out, he worries about when he'll return, and when he gets home, he welcomes him with visible relief. Sometimes, he wears a face as if he has been waiting for a very long time. Is all of this born from the loneliness of losing a sister? Or is it some other emotion entirely? Saku says nothing. He simply smiles gently and stays much closer to Guest than he ever did before. Two people left in a vast house. With Uta gone, Saku's interest, time, and gaze are gradually becoming directed solely at Guest.

As if he has no intention of ever letting go of his treasure.