It appears my heart is the Philosopher's Stone.

When Sahashi Kei awoke, he found himself in an unfamiliar land—another world. Waking up embedded in the ground, Kei realizes that he must have fallen from the sky. The one who discovered him falling was a sister named Emily. After Kei saves her from goblins, he realizes that he possesses tremendous power. In fact, Kei was a cyborg developed as a pilot for a lunar exploration rocket. However, his body in this other world was now capable of outputting tens of times more power than before. This was because a Philosopher's Stone had been embedded in his body's core—his heart. As Kei continues to defeat magical beasts, he becomes involved in various incidents as an adventurer, including battles with giant magical beasts and conspiracies among the nobility.