Tamotsu Kodate serves as a mechanic for the Alvis organization, maintaining and deploying defense systems. He transports Soushi Minashiro to Tatsumiyajima Island and provides him with a significant book. During an early Festum attack, he coordinates with Kouzou Minashiro to unlock weapon systems, authorizing the Railgun despite controllability concerns.

His responsibilities later expand to include collaboration on the Gobain manga project with Ian Kamp. He expresses surprise at Canon Hazama's engineering ambitions and considers retirement to complete the manga, a task requested by Ikumi Nishio. In strategic meetings, he opposes risky proposals like deploying Mark Nicht and Mark Sein due to safety concerns but ensures their activation when overruled. He participates in retrieving cores from the Well of Urd and supports converting Fafner units into Salvator Models for critical battle preparations.

Technical oversight remains central to his role, managing color customization requests for Fafner units and supervising engineering teams during combat. He voices apprehension about Mark Nicht's instability, suggesting its disposal in the ocean, yet complies with directives to repurpose it for missions. He assists in relocating the Achilles unit to Misao Kurusu's ship under hazardous conditions and later remarks on the formidable nature of the Mark Alles Salvator Model.

He joins the Second Plan L decoy mission and the Sixth Operation Azure. Returning to Tatsumiyajima after five years, he visits his home, noting dust accumulation and a family photograph. He participates in the Tanabata Festival and oversees final departures from the island. Personally, he explains emotional tensions between colleagues and expresses weariness about prolonged engineering duties while assisting with CDC operations due to staff shortages.