@Rayodino @Claith Or generally the desire to get new friends to not be so lonely. Actually, I have this theory where the power of a host depends not just on the strength of the desire, but its purity as well. Generally one chosen to be a host will be relatively greedy and their power will be on the curve, but Yuko's is selfless and pure, providing the OP levels. Next is Koyomi who also wants friends, but he goes about it in an egoistic way, so he loses to Yuko. It's quite possible that Yuuga's power up is due to his desire changing - going from a selfish wish, to a more empathic one+his desire to protect Yuko. Similarly Rei went from having no desire, to a pure desire, thus, maybe getting the power necessary to overcome Koyomi's defenses.