Girls Bravo Romance15's

Yukinari Sasaki is an average high school student who is frequently ridiculed by girls to the point that he developed an allergic reaction to them. As a result, he breaks out in hives whenever he comes into contact with a female. One day, when he returns home from school, he is kicked into his bathtub by his neighbor Kirie Kojima, but is transported to Seiren, a mysterious world with a mostly female population. He befriends Miharu Sena Kanaka, who ends up following him to Earth. Other Seiren girls with various motives soon visit and join the household. They are taken on many adventures as Miharu discovers the wonders of Earth.

[From Wikipedia]