Astralfice by ForLackOfStars

Sentineling: An underground competition in which participants pilot enormous robots in brutal boxing matches. The tournament takes place once per year, and is colloquially known as the most dangerous sport in the world.

Astralfice tells the story of Astrid, a sheltered young mechanic with intense social anxiety. In her search for work, she is unwittingly sucked into the world of sentineling, becoming part of one of the teams in the competition. As her team members take Astrid under their wing, she struggles with keeping her anxiety a secret, figuring out how to maintain the first friendships she has had in a long time, and the discovery of a dark secret that threatens to tear her newfound family apart.