You know, Yamazaki Kento-san was actually on the cover of 『Housou Kinshi.』 as Tanabe-kun~. Then, he was still in his teens. So young!
This can be read on Every Star ⇒ 「Housou Kinshi.【Conclusion】」 See you, Sensei. After school on Thursday, at the usual place. #everystar https://estar.jp/_novel_view?w=22781703
The two images that Sakuragawa Sanagi shared in her tweet above are from Vol. 1 back, and Vol. 2 front cover. Kento is also on the back of other volumes, like this one from Vol. 3: