Putative transcription factor, that seems to be involved in anterior-posterior patterning of the slug, probably by controlling the proportions of prestalk and prespore cells. Specifically expressed in pstA cells. Expression is not detected in pstO or prespore cells. Cells show an approximately 2.5-fold increase in the number of pstO cells and the size of the pstO domain and a concomitant decrease in prespore cells and the size of the prespore domain. 'Wariai' means 'proportioning' or 'ratio' in Japanese.