Asobi ni Iku yo!, Haiyore! Nyaruko-san Recommendations
An alien girl comes to the Earth and falls for the protagonist, other girls come into the picture and a harem ensues. Lots of action, sci-fi and ecchi in both ones, not forgetting the comedy. First series coming to mind when watching Asobi Ni Ikuyo was definitely Nyaruko-san. Also, both protagonist alien girls having something to do with cats.