The tale of a modern day 'otaku' (Japanese for fanboy/geek), who stood up to a drunk who was harassing a woman on a train, and the geek's attempts to get the girl.
It has spawned a TV show, a movie, and countless manga adaptations, and is truly legendary in modern Japanese culture, despite being supposedly a true story. Whatever it's origins - it is a funny and heart-warming tale of faltering love from the perspective of an inexperienced guy.
I suspect this will be more popular than the other perennial Japanese favourite, Socrates in Love - which I'd also recommend readers to check out.
Personally though, I bought this, and then have bought 2 other copies for my girlfriend, and my best mate, and recommended the book to countless others. Buy it, you really won't regret it.