Tsukita Gen

In the other world, wield Earth’s knowledge as your weapon! On Earth, use magic from another world! A grand rise-to-power fantasy where a soul is shared across two worlds!! Dennis, the second son of an impoverished noble family, one day realizes that he shares his consciousness with Masaya, a middle-aged man from another world (Earth). Though initially bewildered by this bizarre situation, Dennis quickly recognizes that Masaya’s modern knowledge could be the key to restoring his territory’s failing economy. Determined to save his family and the people of his domain from ruin, Dennis begins taking action using Earth’s knowledge and innovations, while Masaya gains access to magic in his own world…!

I'm not "useless"! I'll prove it by conquering dungeons! Suddenly, magic and dungeons appear in modern Japan, and life has changed completely. I, Midorimu Sakaki, am born with a talent for life magic that cannot be used for exploring dungeons or defeating demons. I was born with a talent for life magic, but while exploring dungeons, I got my hands on a rare item, the "Sage System," which allows me to create new magic...?Web Novel (jp)