In total, it took the kid about a year to produce his fan-made Attack on Titan volume, and it’s not his only project of this type, as @moriteppei says he also redrew an entire volume of the Seven Deadly Sins manga.
…and see that he’s recreated an entire volume of the manga, frame by frame!
“Honestly, his art already looks almost as good as the actual early issues of Attack on Titan’s did.”