Ai to Ao no Kyoukai

Aiko Uozumi, an employee at Rainwater bookstore, is 29 years old and single. Despite her family pressuring her to "get married soon," she lives life at her own pace. But one day, Aiko is frightened by a young man staring at her at work. However, it turns out that he's her cousin! Moreover, they're going to live together?!

(Source: Gentosha Comics, translated)