I Summoned Her!? is a Manga/Manhwa/Manhua in english language, Ecchi series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

Yuta Agatsuma is a high school student who has never experienced first love. He doesn't know how to fall in love, but his classmate Nodoka Kanzaki is someone who makes him interested. Is this love!? Meanwhile, his younger sister named Yoru, who dreams of summoning demons, is performing her summoning ritual as usual. At that time, the summoning circle suddenly shines and a girl descends from the sky... She is Lars, a demon from the demon world, and she offers Yuta a contract...!? A thrilling 7-way love comedy where cheating = the end of the world begins!