Wawawa!! is the third chapter of the Dollars/Mika Harima Arc.
The Black Rider heads to her home after the dispute with the human traffickers and is greeted by her roommate Shinra Kishitani. Shinra asks her about her job, and taking her silence as a confirmation he makes an off-hand comment that Izaya Orihara's information was useful for her job.
The next day Mikado Ryugamine is attending the welcome ceremony at Raira Academy and later in class is intrigued by one of his female classmates, Anri Sonohara. He notices that Anri is looking in his direction, specifically at Mika Harima's empty seat behind him.
After school is over, Masaomi approaches Mikado and offers to take him to any place he wants to in Ikebukuro. The two head over to a manga store, where they meet two acquaintances of Masaomi - Walker Yumasaki and Erika Karisawa.
The two boys leave the book store and as they walk around thinking of a place to eat they encounter a Russian sushi chef, whom Masaomi introduces as Simon and a nice but dangerous person he should not cross. Just as Masaomi is mentioning dangerous people for Mikado to avoid, they are called out to by a man named Izaya Orihara.
Mikado: "And on my second day in Ikebukuro, I cam face-to-face with that very person."