Man, I love this manga.
This seems like it's a heart-targeting thrust, it would be a lethal move in a more severe setting. That being said, has Yodaka killed people before? The tone of the manga has kind become pretty light-hearted but I'm pretty sure he nearly decapitated the first guy to try and capture Aoi, or maybe it was just a hallucination. (The guy had a vision of his head being sliced off by a swipe, but Aoi turned around and Yodaka stopped.)