Y-o-ongi's manga / #strong male lead(6)

he, his sister, mom, and dad went somewhere on a plane, and it crashed. his sister survived and went back home to their grandfather thinking that everyone died except for her. her brother also survived but went to combat training for years. he finally remembers her and got in touch. also there's bullying, but two of the bullies are now friends with the MC and his desk mate.