My Monster Secret Vol. 1 (manga)

Everyone knows Asahi is the worst liar in school–he's so painfully transparent that his childhood frenemy has developed gossip tabloids around his best kept secrets. When Asahi falls in love with the enigmatic Shiragami Youko from his class, he decides to confess to her before she, and everyone else, can read his feelings like an open book. There's just one problem–Asahi stumbles upon her secret, and it's a lot bigger than his! Youko is, in fact, a vampire, and if the school finds out, she'll disappear from his life forever.