He showed up in volume 7. He’s the son in the Australian family who Natsuki stays with when he goes there every year. He comes to their town to visit (he’s been living in japan for a while, but wants to move to Tokyo) and ends up staying with them, and then eventually he goes and lives in Kurisu’s house. When he meets Kurisu, he thinks his name is Kris, and comments that his friend back home is also called Chris. That’s who this is! He came to visit Alex in Japan, this is the first time we meet him.
He showed up in volume 7. He’s the son in the Australian family who Natsuki stays with when he goes there every year. He comes to their town to visit (he’s been living in japan for a while, but wants to move to Tokyo) and ends up staying with them, and then eventually he goes and lives in Kurisu’s house. When he meets Kurisu, he thinks his name is Kris, and comments that his friend back home is also called Chris. That’s who this is! He came to visit Alex in Japan, this is the first time we meet him.
this chapter is the source for all that - https://www.mangago.zone/read-manga/blue_sky_complex/mh/to_v-7-chapter-32/pg-1/