If you haven't figured it out yet, the first character is the only one you unlock that way (besides Helen). For everyone else, you have to click on the college button on the center-right, then click the girl icon in the lower-left to increase loyalty. Once one of the buildings gets its bar full, you can click on it to unlock another character (or sometimes a single CG). Just keep in mind there's a bug where, sometimes, a building will say it's "ready" at the wrong time (it could be either you need more loyalty or that it's just completely done).