Born with a supernatural gift for climbing, brooding loner Mori Buntarou, ascends the highest mountains in order to escape from the world below. For most of this manga there's nothing waiting for him below. He's a misanthropic misfit who has been hurt by anyone he's ever opened up to, so he prefers to do everything solo.
Moody loners protagonists are a staple of manga. Usually they are presented as mysterious badasses who make women swoon without having to utter anything more than a grunt.
Like Client Eastwood, they are cool.
I'm sure many young men have tried to emulate that sort of suave detachment in real life and (hopefully) learned that it makes them seem like awkward weirdos. Therefore, I usually find characters matching that description to be bland and unrealistic, but in this manga Muto's characterization subverted my expectations. He's weird, and turns people off. Regardless of how many mountains he conquers, he's a social outcast who can hardly do more than stand speechlessly when faced with another human being.
Instead of worrying about that, Muto obsesses over a single Herculean task "Climb the highest mountain", which he writes down and pins onto the wall of his austere single room apartment. There he lives like a monk, carrying a heavy ruck-sack full of water bottles to and from work because he doesn't have running water at home (or any other essentials). He cuts back on food for days, and bivouacs in the dead of winter because he has one thing in mind: to conquer the untrodden East-face of K2.
A major theme of isolation and the risk of opening oneself up to others persists throughout this series. I won't spoil it for you, but I'll mention that as soon as the once suicidal Muto finds acceptance and love, he finally finds what he was looking for on those mountains.
