MUGEN is an open-source gaming engine that permits programming-savvy users to have any fictional character fight almost any other fictional character, from ones licensed or created for fighting games, to ones who have been in video games but not fighting ones, even to ones who have made no video game appearances, though these involve the most effort.
As with many another fighting game, even a character who is low in power in their stated world may engage and defeat foes who they would logically in-story have no chance against, leading to some absurd battles. The Avengers' archer Hawkeye could defeat Superman or Dragonball's Vegeta, only to be trounced by Nellie Olsen from Little House On The Prairie. Since it involves licensed characters, this engine is frowned upon by much of the legal and licensed gaming community.
Lucy is among these. She is capable of using close-in and ranged telekinetic bursts, and like many current fighting characters, she builds up over time a series of even more powerful attacks, that, if timed properly, can end the round very quickly. In fact, she may be regarded as a 'cheap' character, one so powerful that other players shun those who use her, but since the engine is open, there are other characters of similar power.
Also in keeping with many current fighting games, Lucy may engage the brief use of a helper character. In her case, one is a man who looks somewhat like Kurama, story issues aside, and the other is Nana, who helps set up the opponent for more strikes from Lucy. In one of her winning animations, Lucy is seen standing while Nana runs up and slips on all the blood spilled by her victory. Lucy also is known to say Kouta in both victory and defeat. Her game 'ending' shows scenes from the anime finale.
Lucy and Nana's images are approximations, since a major release of an Elfen Lied game has yet to occur.