This is me being stupid but I'm so confused! Apart from the summary and grandpa Sho used t...

the story happens in the present, basically those two students were their past selves, their present selves (they're teachers now) start remembering who they were and their past selves and in that process they start getting confused about who they are because their sense of self is getting mixed up with who they were in the past and that's why the seme kinda shifted conscience with his past self. eventually they learned to separate their current selves from their past. their past selves died in a mine explosion

Thank you! Now I understand it