Formally identified as Letter the 15th, he leads the Inquisitors and is a direct descendant of Silvio Letter, the economist who founded Chimney Town's societal structure.

Silvio Letter originally developed "The L," a unique currency designed to decay over time, intending to combat greed and economic inequality. This system restored peace until the Central Bank, threatened by its principles, executed Silvio and abolished the currency. Silvio's son then led rebels to establish Chimney Town as an isolated refuge, constructing massive chimneys to generate perpetual smoke shielding the town from external influence and perpetuating the ideals of "The L."

As the 15th successor, Letter oversees the Inquisitors, a white-uniformed police force enforcing conformity and suppressing dissent within Chimney Town. They actively censor knowledge of the outside world, particularly the existence of stars beyond the smoke barrier, and eliminate perceived threats—including the murder of Bruno, Lubicchi's father, for spreading forbidden knowledge. Despite his authoritative role, Letter exhibits reluctance or ambivalence toward his duties, contrasting with his more zealously antagonistic subordinate, Toshiaki. This positions him as an heir to a legacy of control.

His narrative function embodies the consequences of his family's ideological legacy: the smoke represents both physical isolation and the perpetuation of a well-intentioned yet oppressive system. His lineage directly connects Chimney Town's origins to themes of economic idealism devolving into authoritarian control, framing him as a symbol of institutional power upholding the status quo.