Hayate no Gotoku!!

Synopsis

Father Linn Regioster suddenly appears before Hayate and announces his decision to rest in peace. However, he claims that to finally leave the Earth, he must rid himself of his one lingering regret by flirting with a maid. Since Maria cannot see Linn and because Hayate has no intention of letting Linn take over his body, Isumi resolves to learn how to be like a maid herself. After Nagi coaxes some advice out of Wataru under dubious circumstances, Sakuya introduces her new maid Haru to teach Isumi the spirit of a maid. Much to both Hayate and Isumi's chagrin, however, the entire setup was an April Fools' Day joke by Linn. Later, Haru is revealed to be Chiharu Harukaze the secretary of Hakuou Academy who doesn't want her secret expose to the others.

(Source: Wikipedia)