Amatatsu and Sen of the 'Zombie Hide Sex' world also met when they were in highschool, there's a photo reference in the other manga in 'Zombie Hide Sex' world where, the main characters, Haruomi picks up an old photo of Sen and Amatatsu in highschool. The photo is similar with the Sen and Amatatsu here has, but has different posing. The Photo from the Zombie hide sex world Sen was not smiling like their other photo here (possible indicating that they weren't in a romantic relationship yet, but Sen seems to have hidden crush on Amatatsu in every world.)
Adult Sen in post- apocalyptic world also hinted that they ended up in the same company by coincidence and met again. Sen also said that then Post-apocalyptic Amatatsu would visit his workplace with a banquet of roses. (In this timeline, their relationship probably started late, and was also initiated by Amatatsu like in alternate world, where Amatatsu confronts Sen about his feelings and his experience in the other world, so they became a couple.
Amatatsu and Sen of the 'Zombie Hide Sex' world also met when they were in highschool, there's a photo reference in the other manga in 'Zombie Hide Sex' world where, the main characters, Haruomi picks up an old photo of Sen and Amatatsu in highschool. The photo is similar with the Sen and Amatatsu here has, but has different posing. The Photo from the Zombie hide sex world Sen was not smiling like their other photo here (possible indicating that they weren't in a romantic relationship yet, but Sen seems to have hidden crush on Amatatsu in every world.)
Adult Sen in post- apocalyptic world also hinted that they ended up in the same company by coincidence and met again. Sen also said that then Post-apocalyptic Amatatsu would visit his workplace with a banquet of roses. (In this timeline, their relationship probably started late, and was also initiated by Amatatsu like in alternate world, where Amatatsu confronts Sen about his feelings and his experience in the other world, so they became a couple.