This ritual borders on a romantic act, which is distinguished by being a surprise, and primarily in service to one person. What makes King/Queen for a day a couple ritual is that it is planned, recurring, meaningful, and reciprocal (meaningful to both).
For that day (or hour(s)), your mate has royal power to command you as s/he wishes. Offering absolute power requires absolute trust, and the reaffirmation of that in the act (regardless of what the requests are) is very powerful. One couple made special tokens that could only be cashed in once every two months