Mars

The fourth goddess to be revealed in the series, Mars resides in Yui's body. When Mars takes over Yui's body, her hair becomes lighty tied into a braid and wears a ring headband. Unlike her sisters, Mars has just recently woken up after Yui started dating Keima when the latter agreed to cross-dress. As a Goddess of War, she is very cautious going into any new situation and always suggests Yui to bring a weapon and is a little perplexed by Yui and Keima's cross-dressing; she had first mistaken them for a boy and girl, respectively. While she has just gotten to know Yui recently, Mars fully supports Yui's love for Keima. When she uses her powers, she can summon a magical rapier.

(Source: Wikipedia)