Gaishuu Isshoku Raw !full! -

If you are looking for a specific manga titled "Gaishuu Isshoku" , it is likely a niche or fan-coined title. However, the concept permeates works like "The Horrors of a Gentle Wife" (webcomic), "Ijimeru Yabai Yatsu" (The Dangerous Bully), or "Killing Stalking" (Korean, but follows the same principle). Searching raw manga aggregators with the Kanji 外柔内食 may yield specific results.