WHAT? Why would you try to stop it when you can just create a little wall or something with L shape and just stand on it while his barrier in L shape is being pushed by the spinning doors.
@bvdaf because the authors story is one giant derp.
"if i die, i need you to take care of my sister, if she dies, everyone dies"
"can you explain that"
"Sure after i risk my life doing the one thing that lead me to ask you to look out for her"
Also, Why would the MC think that his sister getting killed would kill everyone? There is absolutely nothing to support that! At most he might be able to say "if she dies, its possible we could die too since this world resembles her book, its possible she has some power of this world", but its equally likely that its some god screwing around and he simply used the sisters story as a theme.