haiyore! nyaruko-san
A 2009 light novel series written by Aisora Manta, illustrated by Koin and published by GA Magazine. Also adapted into two ongoing 2011 manga in Shueisha's Miracle Jump by Okazaki Kei, and Haiyore! Super Nyaruko-chan Time in Flex Comix Blood by Hoshino Souichirou, as well as two flash ONAs, Haiyoru! Nyaruani (2009) and Haiyoru! Nyaruani: Remember my Mr. Lovecraft (2010) by DLE, and a Spring 2012 anime adaptation by Xebec.
After being saved from a fearsome black creature, 17-year-old high school boy Yasaka Mahiro ends up with three freeloaders in his house straight out of the Cthulhu Mythos: Nyarlathotep, the silver-haired girl who saved him, Cthugha, the former's crimson-haired childhood rival/friend, and Hastur, an effeminate blond boy.