World setting: In the same place on Earth, there are Ethereal mutations. Ethereal mutations happen when you stay in Hollows for way too long. There are powerful Ethereals and weak Ethereals among the mutations.

Bangboos are artificial life forms with distinct personalities, found everywhere throughout the city. According to the lore, the first person to develop Bangboos was the CEO of the Marcel Group and a legendary Void Hunter called 'The One Who Brought the Sun.' Originally designed as rescue robots to investigate Hollows and dangerous areas humans couldn't enter during Hollow disasters, guiding survivors to safety. Over time, they evolved into multipurpose robots used across various industries and daily life. However, since Bangboos don't have Anomaly Mastery stats, they can build up attribute anomaly but don't contribute to anomaly damage - Bangboos alone can't trigger anomaly states. They typically only make 'ehn' and 'na' sounds, but communicate by combining these words in different ways. It's a seemingly bizarre language unified in-game as 'ehn-na,' but translation devices for Bangboo language exist, so most citizens can understand them. However, not everyone gets Bangboo speech - there are scenes with Bangboos that have broken language modules or elderly people who can't understand them. Among Outer Ring residents cut off from the latest tech, you'll hear complaints like 'I bought a new navigation plugin but it just goes ehn-na and I can't understand it.' Since they have real personalities with emotions, they sometimes use colorful profanity too. A signature trait is how they run - stretching both arms straight up and scampering super fast on their tiny legs going pitter-patter-pitter-patter. They're absolutely adorable in person. The protagonists Belle & Wise have unique H.D.D. technology that lets them sync senses in real-time with Bangboos (Eous) inside Hollows. The legendary Proxy 'Phaethon's' reputation is built almost entirely on this tech, and from in-story descriptions, no investigation guilds or major corporations have this real-time Bangboo control technology. This creates comedy moments where the protagonists imitate Bangboo speech patterns when controlling them, worried that speaking normally would expose their tech and draw unwanted attention.