Elsie Jewelria, Run

A childhood friend of Lala, infamously known for wearing girl clothing during his play dates with Lala. At first he arrives on Earth to win back Lala, but soon becomes jealous due to her relationship with Rito. As Ren is from Planet Memorze, he can change gender in both mind and body upon sneezing; as a girl she goes by the name Run. Run likes Rito, while Ren is in competition (albeit rather one sided) with Rito for Lala's hand in marriage.

In To Love-Ru Darkness Run and Ren are finally separated from each other. It's also revealed that Memorzians may separate when reaching adulthood.

(Source: Wikipedia)