Uke was sent as replacement concubine of neighboring kingdom because of prophecy that she would live a good life (prosperous) if they send the person from the prophecy to the kingdom as her replacement (the uke). The king (seme) notices he is not the real concubine but started to fall in love (feel special) toward him and possibly be reencounter moment from someone in the past. Uke is able to calm the headaches of seme which is why seme starting to fall in love
The Concubine is a man