Neco-chan

Basically mc got his whole memory back, the one he lost of his time in this world and the one from before he got here(transmigrated/reincarnated). He realizes that the sunbae and ml are the same people and he remembers how he and why he transferred? Here.
This also explains mcs constant illnesses and the coughing up blood thing because I guess he isn't fully dead in real world and is being crushed to death, hence the leg pain in earlier chaps

Thank you you beautiful angle