Both have two effects: one which alters their ATKs for the duration of two turns, and another effect.
Interestingly, their effects, like their ATK and DEF, are also reversed (this card's ATK-gaining effect must activate after its previous effect has resolved, while Vixen's ATK-gaining should be activated before its other effect).
In their artworks, both are facing reverse directions to one another; also both artworks contain a noticeable arc, which are also on opposite sides of the artwork. This further indicates a yin-yang relationship between the two.
Although more coincidental, the two are consecutive in alphabetical order in a List of Xyz Monsters. Also, they were released in consecutive sets.