This is episode 1 to VII -Invitation to Madness-
Invitation to Madness[]
After having being awakened under a bridge, a man with no memories nor name saw in front of him to be a girl. She had introduced herself to be Yuki Shiro, a 2nd-year student in high school. After they had talked to each other for awhile, the nameless man had noticed the Roman numeral "VII" on his left hand and, without thinking, introduced himself as Nana (meaning: "seven" in Japanese). As they continued talking, time had passed and had skipped to the next day at Yuki's school. Once Yuki had met with her friends Hitomi and Sakura at school, Yuki had told them about Nana and had made Hitomi and Sakura suspicious. After school had ended, Yuki had introduced Nana to Hitomi and Sakura, and as Sakura immidiately fell for Nana, Hitomi still had her suspicions.
As a few days pass by, Nana had been visited by those three girls for those last few days. At the seventh day of the visit, Yuki had met with Nana by herself. Yuki had explained why her friends couldn't visit him that day then had another long talk with Nana. After awhile, Yuki had fell asleep for a few hours and had later woke up around 10 at night only to have another chat with Nana, but this time, she told him that if he ever needed a home, he should stay at her house since her parents are really nice. As they continued talking, a spider-like monster in another area of the city had appeared and went through a path that was going towards the bridge after having killed dozens of people. Not knowing what going on in the city, Nana and Yuki were carelessly talking with each other as usual but right when Yuki was about to tell him something, the monster had suddenly appeared and stabbed Yuki in her stomach, putting her in the brink of death.