[Snake]

Did you target them with Sheath Sword before using? I mean, the blue square that shows one tile is selected. If yes, that will (FOR SOME REASON) proc Geist Schritt, as you are targeting the enemy with it.

Sheath Sword has a 1 tile range, instead of 0 like let's say, Shukuchi, or Charge. It allows you to target the enemy as the 'range selection' points under the enemy's square, and Geist activates there.