Durarara!!

From Yen Press:
At the invitation of an old school friend, introverted high-school student Mikado Ryuugamine, yearning for a life less ordinary, makes his way to Tokyo. His destination: Ikebukuro, a hotbed of madmen living most unusual lives. On his first day there, Mikado encounters a cast of characters so colorful, the rich hues of his rural hometown pale in comparison! And as if the naive stalker chick, the high school senior obsessed with the rather creepy object of his affections, the hikikomori genius doctor, the hedonistic information dealer, the strongest man in all of Ikebukuro weren’t enough…Mikado also chances upon a sight that leaves him rubbing his eyes and scratching his head — the Black Biker, who is black as night from bodysuit to license plate, soundlessly weaving through the streets like a figure out of an urban legend. Who is this “Headless Rider” on the jet-black metal steed!? And why does it seem like Mikado’s already gotten himself neck-deep in the insanity that is the norm in his new home!?

1st Arc: Durarara!! (4 Volumes)
2nd Arc: Saika Arc (3 Volumes)
3rd Arc: Yellow Flag Orchestra (3 Volumes)
4th Arc: Akane Arc (still ongoing)