The woman you see in the picture is Elluka Clockworker (Luka) but in blonde version. Rgveta already said that the video might be a little confusing for those who haven't read the novel of Aku no Musume. Chrono Story has a very strong relation to the 7 Deadly Sins series. mothy already said in the blog, that Chrono Story set time after Okizari Tsukiyoshou (sung by Rin/Len). If you're a fan of mothy's work, I'm sure you already know about it. Okizari Tsukiyoshou itself is a sequel of moonlit bear (sung by Miku). So the chronology is: moonlit bear - Okizari Tsukiyoshou - Chrono Story. So To make it more clear, I'll write from the very beginning ^^;
First, in moonlit bear, Miku was a woman who had married with Kaito, The couple ever had a child, but their child died. One night when the full moon shines, Miku "stole" Rin and Len from their mother (Meiko). At first, Rin and Len was represented by "two fruits" which Miku found in he corner of the forest while Meiko was referred as "bear". Not just taking her children, Miku also killed Meiko.
Then in Okizari Tsukiyoshou, Rin and Len grew up with Miku and Kaito. But one night, the twins were left in the forest by their "mother and father". The twins didn't know the way home and followed a twinkle light. They finally arrived at a home that they think was a cruel witch's house. Actually, the house was their own house but they didn't realize it. They ended up killing Miku and Kaito and then they wanted to search their "real parents".
Finally, in Chrono Story, Rin and Len already killed Miku in the fireplace (perhaps along with Kaito). From Chrono Story, it is revealed that the "Original Sin" is originated from Miku (the twin's "Mother"). Then the twins divided it into 7 deadly sins. The 7 deadly sins then spread to all over the world. Elluka Clockworker was a sorceress here. The Tree of Eldo, asked her to collect the 7 Deadly Sins. Looks like she didn't mind being asked to do so, she also said, "I don't mind as long as it keeps me entertained. I have unlimited time anyway." Elluka herself, in this song, is told as a sorceress who lost her beloved one but she gained eternity. But the eternity itself made her felt empty. In the end of the video, Elluka arrived in a castle. Probably Venomania's castle. Duke Venomania also appears in this video. Maybe we can assume that Duke Venomania made a contract with Elluka to atrract women.
Although Chrono Story is an English titled song, this title is actually a perfect pun by mothy. Chrono Story in katakana is like this: 『クロノ・ストーリー』---> Kurono-Sutoorii --->Kuro no Story ---> Black Story. A perfect pun, isn't it?
I hope this post will help. Since I didn't manage to get Aku no Oukoku booklet scans and the novel, I admit that I myself have some confusion about this. So if you already read it and find some mistakes in my post, feel free to tell me ^^