If you're hoping for a cosplay show that lives up to My Dress Up Darling, you will be disappointed. In many ways they are opposites, with MDUD invariably taking the more interesting fork in every road. 2.5D Seduction spends no time on the process of making a costume or improving the related skills, since Ririsa pops up in episode 1 having already made the perfect costume that will capture the heart of anyone who sees it. That's lucky for her because she has no interest in cosplaying as any other characters, so she trots out this costume again and again, while wowing people with it again and again. We're occassionally told that she's wearing different costumes for the same character, but they're so close to identical that I couldn't spot any differences. These costumes just pop up fully completed anyway, so it doesn't tell us anything new about Ririsa or her skills. Another major aspect of the show is cardboard protagonist Masamune photographing her, which he does with an expensive camera that Ririsa just happens to already own, so again there's no development arc and no learning. Stuff just happens.
So what does the show spend time on? Mostly it's cosplayers hanging around at cosplay events, silently monologuing to themselves about how they feel about cosplay (including flashbacks to their past cosplay-related traumas, of course). When the show reached a point where an entire episode was just two side characters standing next to each other in a crowd of photographers, silently monologuing to themselves about their cosplay backstories, my eyes glazed over and I dropped the show.
The only reason I'm not rating this show lower is because the early episodes do get some mileage out of the faltering romance aspect of Ririsa cosplaying Masamune's favourite waifu, but that runs out of steam after a while.