A new and distinct cultivar of Chrysanthemum plant named `Yothersea`, characterized by its compact, upright and outwardly spreading plant habit; freely branching habit; dense and full plant habit; uniform and freely flowering habit; daisy-type inflorescences with elongated oblong to ligulate-shaped ray florets; purple-colored ray florets; and natural season flowering about September 21.sup.st in the Northern Hemisphere.