I like the plywood to tie it in to the lower wall. you guys are right, storage behind this wall, but there is gonna be a matching (but longer) wall on the other side of the stairs that will see a teenager boys traffic to his room and all of his friends, etc.. so any techniques will be applied to that side too. Keep the ideas coming.
1983 Honda CB650SC Nighthawk
1984 Honda GL1200A Goldwing Aspencade, a work in progress
1996 KTM 300 EXC Plated