Durarara!! Episode 9 -

If you are watching the later seasons, here is a quick guide to their respective 9th episodes:

It is revealed that Mika Harima , who had been stalking Seiji, discovered the head in his apartment. In a fit of rage and obsession, Seiji killed her. Namie later had the head (supposedly) surgically attached to Mika’s body. Durarara!! Episode 9

Amidst the chaos, the girl escapes and runs into Mikado Ryuugamine , who hides her in his apartment to protect her from Celty. Notable Adaptations & Differences If you are watching the later seasons, here