Ikebukuro's Most Dangerous is the third chapter of the second Durarara!! light novel.
Shuuji Niekawa is tasked to write an article with the theme 'the strongest in Ikebukuro' and sets out to interview various residents in the city for their take on who it could be, gaining testimonies primarily from: Haruya Shiki, Denis, Izaya Orihara, and Celty Sturluson.
While Shuuji initially dismisses the first mention of Shizuo Heiwajima's name, after each person testified Shizuo to be the strongest and hears of his superhuman feats, Shuuji manages to get in contact with Shizuo's boss, Tom Tanaka, to set up an interview with him. Upon meeting Shizuo, he has trouble believing Shizuo to be what everyone says he is based off his demeanor and forfeits Tom's warnings, provoking Shizuo to witness his rumored strength and resulting in him getting thrown across the room.
Afterwards, Shuuji is awed by Shizuo's ability and is inspired to write an article on him. However, later that night he is rumored to have been attacked by the Slasher. Kanra brings up the incident in the chatroom when the user Saika logs on again, spamming messages of wanting to cut more people and wanting to find Shizuo Heiwajima.
Haruya Shiki (about Shizuo): "When you watch him fight, he looks cool the way that Godzilla looks cool to the kid watching it. I guess that sums it up. At any rate, he's one crazy bastard. ......Gotta admit, I've got some admiration for him. Wish I could tear things up the way he does."
Celty (about Shizuo): "That's it - his strength is like the power of a gun. Even comparing him to others makes no sense."