Isekai no Sata wa Shachiku Shidai

Seiichirou Kondou, a salaryman approaching his 30s, gets caught up in a holy maiden summoning ritual and is transported to a parallel world called Romany Kingdom. Having worked day and night, he developed the mindset of a corporate slave and even demanded work in this new world, which landed him an accounting job at the Royal Accounting Department.

During his hectic days rebuilding the accounting department, Seiichirou came across a nutritional tonic that wiped away any fatigue. Thanks to the tonic, Seiichirou's chronic ailments and exhaustion completely disappeared, leaving him overjoyed. But because he had no resistance to the world's magic, the side effects put his life in danger!

The only way to survive was to have someone with magic help accustom his body to magical energy, so with no other choice Seiichirou entrusts himself to Aresh, captain of the Third Royal Order, known as the Ice Prince.

(Source: Crunchyroll)