based on my own grandfather. pure dialogue.
ace walks off after exploding because marco read the newspaper wrong while luffy is visiting.
'why is he like that?'
'ace can't read. he can read bounty posters but thats about it. and people lied to him as result of not being able to read.'
'hes tried but its never worked out. ace has fought for everything he knows. he learned manners from makino painstakingly, it was what he wanted to do, to thank shanks for saving me. but it was hard for him.'
'he grew up surrounded by mountains bandits. even they had trouble reading the newspaper. and gramps wasn't much better, he could barely write but he taught us all he knew anyway. so we'd be more prepared than he was.'
'when gramps joined the navy, they sent him to war, they didn't care if he couldn't read or write and now thats hes old, he doesn't really see why he should learn.'
'but i know he tries, makino tells us he spends hours trying to read our letters, and that hes trying to write more.'
'and sabo. sabo could do all those things. he could read and write. he taught us as much as he could but ace had trouble and i was the only one to pick up on it.'
'and after sabo died, he made me read the letter. after that, ace tried harder to read but even then he couldn't.'