Niche is the dingo and constant companion of Lag Seeing, the protagonist of Tegami Bachi: Letter Bee. She was originally found by Lag as an undeliverable letter at a train station, with an incomplete address and scheduled for disposal. Lag named her Niche and took responsibility for her delivery, but after she escaped the facility called Lovesome Downs, where she was held as the legendary Child of Maka, Lag saved her from Gaichuu territory and she chose to become his dingo. As a dingo, she serves as Lag's bodyguard, protecting him from the giant armored insects known as Gaichuu that threaten Letter Bees during their mail deliveries.

Niche is a young girl with light blue eyes and long, very long blonde hair that she usually wears in two tails. She is small in stature and flat-chested, a fact she is aware of and openly wishes to change, occasionally lashing out at women with large breasts in comedic moments. Her personality is fierce, protective, and straightforward. She is quick to anger when anyone threatens Lag or tries to take her food, but she also shows a deep, loyal attachment to him. She insists that Lag refer to her as Niche, my dingo rather than just Niche, underscoring her pride in her role. Despite her sometimes violent reactions, she has a childish innocence and a strong sense of devotion.

Niche possesses remarkable abilities that stem from her heritage as the Child of Maka, a legendary creature from the north. Her most distinctive combat ability is the power to transform her hair into six long, golden blades that are incredibly durable, sharp, and flexible. When activated, her hair becomes a set of sword-like weapons she uses with great skill and ferocity against Gaichuu and other enemies. Her strength and fighting instincts make her a formidable bodyguard, and she is fiercely effective in protecting Lag.

Her primary motivation is to stay by Lag's side and protect him. Having been abandoned and nearly discarded, she found purpose and connection in Lag, who treated her with kindness when no one else would. This bond drives her actions throughout the story, and she develops a deep emotional attachment to him. Niche also has a twin sister who appears older due to a growth spurt caused by their separation, and her relationship with her sister becomes an important part of her personal story arc, adding depth to her past and her sense of identity.

Throughout the series, Niche remains a loyal and integral member of Lag's team. Her development is less about radical change and more about deepening her trust in Lag and others, as she learns to move beyond her guarded, aggressive instincts and embrace her role as both a protector and a friend. Her relationship with Lag is central, and she also interacts with other recurring characters such as Connor Kluff, a fellow Letter Bee, and carries her pet dingo named Steak on her head, a creature that provides comic relief and companionship.

Niche's notable abilities include her hair-sword combat, her heightened senses and reflexes as a dingo, and her physical resilience. She is also able to sense danger and Gaichuu presence, making her an early warning system for Lag. Her fighting style is aggressive and direct, relying on speed and the unique properties of her hair weapons. Niche's background as a letter herself, her legendary heritage, and her unwavering loyalty to Lag define her as both a protector and a character searching for belonging in a world that once cast her aside.