Matsuemon Tennoji is a Kasugai Crow who serves as the personal messenger for the Demon Slayer Tanjiro Kamado. He is a male crow distinguished by possessing a full name, an uncommon trait among his kind, which he gave to himself rather than receiving from a superior or from Tanjiro. Matsuemon is exceptionally intelligent and talkative, displaying a wide range of emotions and opinions. He has a notably large ego and is openly disgusted by Zenitsu Agatsuma upon their first meeting, believing that a man should attract women rather than cling to them.

As a member of the Demon Slayer Corps, Matsuemon's primary role is to deliver mission orders from headquarters to Tanjiro in the field. He takes this responsibility seriously, ensuring messages are relayed clearly and promptly. His intelligence extends beyond simple delivery, as he demonstrates strategic thinking and deductive reasoning on at least one occasion. He is able to help uncover the location of the demon doctor Tamayo by identifying the previous owner of a house and analyzing the workings of Yushiro's Blood Demon Art, showcasing a capacity for investigation that goes beyond the typical duties of a messenger crow.

In addition to serving Tanjiro, Matsuemon becomes an important source of information for Inosuke Hashibira. Inosuke's own Kasugai Crow, Dongurimaru, avoids him out of fear, so Inosuke relies on Matsuemon for orders and updates on demon locations. This unusual arrangement highlights Matsuemon's reliability and the trust placed in him by multiple slayers.

Matsuemon's relationships within the Corps are defined by his loyalty and his somewhat pompous demeanor. He holds a clear allegiance to Tanjiro and maintains contact with the Ubuyashiki estate. His interactions with other demon slayers often reflect his condescending attitude, particularly toward Zenitsu. Later in the story, Matsuemon's character shows growth; he becomes devoted to another crow named Ginko, participating in a mission with her that marks a shift from his earlier self-importance toward genuine partnership.

Notable abilities include his capacity for human speech, his high intelligence, and his emotional expressiveness, which sets him apart from more stoic crows. His strong sense of identity and willingness to name himself, combined with his strategic mind and enduring loyalty, define him as a unique and memorable presence within the Demon Slayer Corps.