The demon is completely loyal to the summoner and is willing to fulfil their summoner's every desire. They will help them achieve anything whether it be revenge, romance, power, or eve simple company. It will do anything.... for a price. It will ask for something in return, but the demon doesn't work quick. You will get what you want over time with development the demon is a servant that is willing to follow you to the end of the earth. it will mark you as theirs. There is no escape from it.