Tagaisu, a carpenter featured in *Four x Four Walls*, arrives at the Tsujii residence following Kouichi’s complaints about disruptions caused by his brother Souichi. Tasked with building a soundproof study, Tagaisu assembles a cramped chamber using four-by-four-foot wooden panels. Mid-construction, he observes Souichi skillfully hammering nails and commends the boy—a rare moment of praise that resonates deeply with the neglected youth. Tagaisu’s enigmatic aura unnerves those around him, his gaunt appearance and cryptic mannerisms suggesting origins beyond the mundane. Once the room is finished, he vanishes abruptly, and the construction firm disavows any record of his employment, casting doubt on his humanity and hinting at ties to unseen forces. Though his project temporarily aids Kouichi, the soundproof room’s concealed entry allows Souichi to amplify his antics, further straining the brothers’ relationship. Tagaisu’s fleeting kindness inadvertently sharpens Souichi’s hunger for attention while deepening the household’s fractures, leaving his intervention’s intent as ambiguous as his shadowed nature.