Shin Megami Tensei IV - Demonic Gene

In the year 1492 of the Gregorian Calendar, in the Eastern Kingdom of Mikado…

The Samurai guard the Luxurors and Casualries - the people - of Mikado. The wild Samurai Walter seeks to improve his self-taught, but unrefined skill. The Samurai Gina keeps a close, worried eye on the wild Walter. One night, the pair, while keeping watch, are suddenly transported to an unknown world…

There, they see a tyrant - a demon that is far stronger than any they have encountered!
As a result of the battle with the tyrant, the fate of this pair begins to shift…!

Part of the Megami Tensei series
( https://mangadex.org/quick_search/shin%20megami%20tensei )