Elucia de Lute Ima

The World God Only Knows is written and illustrated by Tamiki Wakaki, serialized in the Japanese manga magazine Weekly Shōnen Sunday since April 9, 2008
Elucia de Lute Ima (エリュシア・デ・ルート・イーマ,)
she is commonly known, is the series' Deuteragonist and Keima's partner. Elsie is a 300 year old demon from Hell who has been sent to Earth to capture evil spirits that have escape from Hell as a Spirit hunter. Despite her age, she acts rather childish.
Elsie has a sweet, pure and innocent personality but is rather clumsy and easily distracted which causes Keima to consider her unreliable. Despite these faults, Elsie is always trying to please Keima and convince him that she is a reliable partner.

At the start of the series, she gets Keima to agree to a contract to help her catch spirits through an email and under the belief that he was a womanizer only to learn the awful truth that he misunderstood her email and is actually a womanizer of game girls. However, she manages to convince him that the girls in real life are similar to game girls thus saving both their lives should he refuse.

With her help, she assist Keima in conquering the hearts of girls so she can catch the evil spirits inside of them. In order to be close with Keima without suspicion, she becomes his younger sister(and calling him "Kami-nii-sama"(Divine Brother)) by giving a letter (written by her boss) to his mother, Mari, which claims she is her husband's illegitimate child, living in the Katsuragi household as well as attending the same class as him. Due to her outstanding performance in capturing spirits, she receives an Award for her hard work, much to shock to some of her demon friends who usually know Elsie as a klutz.

Cosplay By Tomia (Korea)
Source:
Wikipedia.