@fizhsmile that is Hiyori. I surprise that you really don't know ?
also when Yat said i have someone i love too: show the key chain -> show Hiyori. I mean, even you don't recognize her. Still don't get why it even relate to Kazuma at this moment
@Tcof I dont think so, Yato talked about Kazuma's past here, he said a girl a year older than Kazuma came to apprentice (possibly came to learn Kazuma's father bussines). Kazuma took a liking to the girl during her apprentice but then she got married off at some point when he was 15. He got broken heart and curled up in a ball then cried. In the page 17, Yato said that he also got someone he love, now this is Hiyori.