The reason why I bring this is up is that in Bayonetta, there is an accesory called the Bracelet of Time. In it's description, it says that Eva, an extraodinary witch, made a contract with a legendary dark night to face the amassed armies of Hell. Naturally, Kamiya added this as a referrence to DMC, but considering that possibility that these two are (unofficially) in the same universe, it could be possible that Eva was a witch ,like Bayonetta and Jeanne, and met Sparda to make a contract with him (In Bayonetta, witches make contracts with demons, commonly demonesses) and the two fell in love as time passed.