Everything Changes
Sonohara pokes Niekawa with Saika, and shows her a flashback of how she became its wielder. Sonohara's father was an antiquities dealer, and constantly beat up her and her family. Her mother then got possessed by Saika, killed her father, and committed suicide. Sonohara then grabs the cursed blade, and becomes its wielder. Meanwhile, Shizuo beats up Niekawa's "Saika children," flashing back to his past. Sonohara then assimilates Niekawa's Saika, and as a result takes control of all of the Saikas in Ikebukuro. Sonohara apologizes to Celty for attacking her back in Episode 5. Mikado later visits Sonohara at the hospital, and after realizing she has met the "unusual people," warns her to stay away from the non-normal. As a result of Niekawa's assimilation, Sonohara has gained her and all of the Saika's memories; she suspects that Izaya is up to something. Mikado is later shown contacting members of the Dollars, but it is unknown for what reason. The episode concludes, as Izaya's plot deepens further; he is revealed to be behind several events in the slasher arc. He has caused a split of the city's population into different "factions;" Saika/Sonohara's army, the Yellow Scarves, and the Dollars; and knows that they will fight amongst each other. Kida, not knowing Anri Sonohara's true nature, retakes his place as the leader of the Yellow Scarves. He suspects the Dollars to be responsible for Sonohara's injuries, and vows revenge.
Aired 07/05/2010EP 17 - Everything Changes

Durarara!!
In Tokyo's downtown district of Ikebukuro, amidst many strange rumors and warnings of anonymous gangs and dangerous occupants, one urban legend stands out above the rest—the existence of a headless "Black Rider" who is said to be seen driving a jet-black motorcycle through the city streets.
Ryuugamine Mikado has always longed for the excitement of the city life, and an invitation from a childhood friend convinces him to move to Tokyo. Witnessing the Black Rider on his first day in the city, his wishes already seem to have been granted. But as supernatural events begin to occur, ordinary citizens like himself, along with Ikebukuro's most colorful inhabitants, are mixed up in the commotion breaking out in their city.
(Source: MAL Rewrite)