Mayo Chiki!

D-Frag!
When Naganuma was described as an otaku, the three anime characters who appear behind him resemble:
 * Charlotte Dunois from IS
 * Kureha Sakamachi from Mayo Chiki!
 * Kobato Hasegawa from Haganai

All of them have the same seiyuu (voice actress), Kana Hanazawa (once seiyuu of Roka Shibasaki), who may possibly be Naganuma's favorite.

All four (D-Frag!, Haganai, Mayo Chiki!, and IS) manga are published by Media Factory's Monthly Comic Alive imprint.

Mirai Millenium

 * anime opening here

Star character Mirai Suenaga (mascot of Culture Japan) appeared most in episode 13 ofMayo Chiki at an anime convention, where she appears along other background characters who resemble ones from other series, including:
 * Azusa Nakano and Nodoka from K-On!
 * Aria from Aria the Scarlet Ammo
 * Natsuru from Kampfer
 * Yuji Sakai
 * Ako and Riko from Kiss x Sis

She first appeared briefly in episodes 8 and 9 though: