See? A burden...he isn't useful for anything. Any dungeon manga I've read up until,
will only bring a weaker player with them if they have some use. Like collecting materials,
to train, etc. But the younger brother is just in the way.
MC can't babysit his brother all the time that's probably why he took him to the castle. But why his brother is just walking around without any weapon or armor is a mystery for me