Watashitachi wa Douka Shiteiru: Shinkon-hen

Six months after their long-anticipated wedding, Nao and Tsubaki spend their free time happily planning their honeymoon. During a wagashi delivery, Nao meets Kagami, a man who runs a poetry club and seems to know Tsubaki. Perhaps even better than she does. As Nao learns more about him and his club members, an attempt is made on Takigawa’s life! Curiously, the attack appears linked to poetry, the exact type that Kagami’s group studies. A few members are convinced it’s a curse, that one of their own is seeking revenge from beyond the grave…

(Source: Kodansha USA)

Note: Kodansha USA published this sequel's volumes under the main entry as volumes 17, 18 and 19.