I've played the guitar for a number of years. While one does need to train both hands, just pressing the strings on the fretboard is relatively easy; the hard part comes when you need to play complicated chords and switch between them quickly. Strumming is simple, but it wears down your fingers pretty easily, especially if you're playing up-tempo and/or without a pick. There's also a big difference between classical guitar (what Haku is playing here) and electric, whose strings are all-steel.