There's this scene in this LN where the main character unexpectedly accepted an invitation to a karaoke, and when questioned about it, the character responded by saying:
Then one character from the rest of the group responded by saying:
I'm not sure as to what "高校生か死神っぽい動機" is supposed to mean
My first guess is that it is something like:
[ 高校生か死神 (か) ]っぽい動機
With the clause in the square brackets being applied to the っぽい.
As in a motive that can either be high school student-ish or grim reaper-ish. But it seems kind of like a stretch.