Go-toubun no Hanayome: Shunkashuutou

The Quintessential Quintuplets: Spring, Summer, Autumn, Winter adapts the official sequel novel penned by Hajime Asano—a work that depicts "the continuation of the original story"—under the complete supervision of the original manga author, Negi Haruba.
Spanning the period from January of their third year of high school through December following their graduation, this series portrays a fresh year in the daily lives of the quintuplets.
(Source: Official Website, translated)
Note: Title and relations are provisional and subject to change.