Apparently all Seiji had managed to do was up the violence. He staggered, damn near falling after Shun's first attack, and a hand was on it's way up, not to counter, but to ward off any oncoming blows. But he didn't get it up in time, never had that chance to throw in the tool. The blade took him across the throat, and there was time enough for his eyes to go wide before he simply wasn't there anymore.
A moment or two later he'd find himself waking up in the nurse's office, throat perfectly whole, and no other signs of wear or tear beside a few cuts to his clothing.