They are playing D&D. With Homuhomu as DM. And she has 3D-printed miniatures. Wow.
Usually it would be CoC. (Whenever you see a tabletop RPG being referenced in Japanese media, it's almost always Call of Cthulhu or a variant. If not, it's some sort of homegrown d6 system like Night Wizard and its ilk. D&D is rare*.)
(*D&D related lore on the other hand is ubiquitous due to AD&D influence on early fantasy series [e.g. Lodoss War, Bastard], as well as early JRPGs like DQ and FF being influenced by D&D via Wizardry and Ultima. But the d20 system itself [and the miniature-heavy playstyle] almost never gets referenced.)