Lemme go over this again...Hotaru's fatality cracks his opponents neck 3 times over. Scorpion's Fatality rips the head and spine out of his opponents neck. Scorpions Hari-Kiri which involves cracking his neck. Hotaru's Hara-Kiri has him ripping his own head and spine out.
Maybe they originally planned it for Scorpion and Hotaru, but at the last second thought it was too similar to their fatalities, so they simply switched it