A new and distinct cultivar of Chrysanthemum plant named ‘Fichryrainsun’, characterized by its upright to outwardly spreading and uniformly mounded plant habit； moderately vigorous growth habit； freely branching habit； dense and full plant form； uniform and freely flowering habit； large semi-decorative type inflorescences with red and yellow bi-colored ray florets； response time about 51 days under controlled photoperiodic treatments； and good postproduction longevity.
