Sensei Wa Kisu Ga Hetana Vampire

Maki Hanai is a 20-year-old university student who is currently on academic leave. On the last day of her part-time job at a coffee shop, a regular customer, a man in his thirties named Otoya Hyakumogi, offers her a job as a live-in employee making vegetable juice. Feeling threatened to her virtue by living with Otoya, a university lecturer in history whose private life is shrouded in mystery, she insists that she has no interest in dating older men. However, after saving him from an accident, she discovers that he is a vampire over 300 years old!

(Source: Kodansha, translated)