Ive been trying ti find it for years and just cant, i think its a one shot within a manga, its about two guys in a bunker cause the outside air is toxic but uke doesnt know that cause hes lost his memory because of a medicine which resulted in his leg needing amputating ( he wakes up on a medical table), he thinks the seme did it out if malice and has locked him up in there but remembers at the end when he leaves and sees the state of the world when seme comes out and puts a gas mask on uke the end