Diago is an ant girl who resides in the monster city Stonegate. There, she acts as a guardian over those who have been taken in, as well as an active fighter who accompanies their raiding parties on enemies in the nearby land.
Unlike other ant girls in the series, Diago dresses in a short formfitting black skirt and sleeveless tunic that's ripped over her large breasts. She wears knee-high black boots, and dark gloves that have steel plating over the fingers, knuckles, and backhands. Her long dark brown hair matches the color of her eyes, her bug antennae sticks out over her messy locks, and her insect abdomen is colored black. She carries a large steel pickaxe with a chain strap to it and also has a coiled chain-link whip holstered on her hip.
In stark contrast to how most ant girls are, Diago is more a warrior than a digger. Hailing from a renowned and feared monster city, Diago proves her right of belonging there with her aggressive and often deadly fighting style. Despite being a fighter and quite intimidating, she has shown compassion to those in need and appears to house a benevolent soul behind her stoic and silent personality.
Unlike other ant girls in the series, Diago doesn't show much interest or activity when it comes to digging. The pickaxe she carries is used for combat rather than mining, and although she is often seen with dirt on her, her role in Stonegate is more of a fighter than a miner. She participates in raids against enemy factions, helps liberate humans who have been captured by more nefarious monsters, and during her time in Stonegate acts as a watchman and general security for the citizens. She's also often seen taking direct orders from the countess, Eirene, to which she complies without hesitation.
Another noticeable trait is that she never speaks, or squeaks, to anyone. It's unclear if she's able to speak or not, however Lucy has made a comment about Diago being a "mute brute", suggesting that Diago may not be capable of talking, in either an ant girl's tongue or otherwise.
- Diago’s character was first designed to be that of a scavenger ant girl who leads a raid on Queen Victoria’s nest at the end of Act XII. She was originally planned to be a villain, with her killing Victoria before the book ended. This was scrapped as a different plan for Victoria and her nest was set by the author, and instead Diago was written as a hero who saves Kroanette in Act XII.