Erlen works in the same lab as Lily as her lab partner. He wanted freedom to conduct experiments, and the terminus was too restrictive for his practices. The wildlife and vegetation varied in each city, so he decided to build underground labs in each city.

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Erlen comes from an old city known as Suri, before it crumbled. He was raised by a family that had passed down medicinal practices. But after seeing similarities between the power dynamics of Suri and Celestia, who denied his passion to study medicine, he comes into contact with researchers in Terminus to poison the current ruler of Celestia.