My Youth Romantic Comedy Is Wrong, As I Expected @ comic, Vol. 18 (manga)

Thanks to interference from Yukino's mom, Yukino and Yui's plans for a Soubu High prom face ruin. But Hachiman has an idea: What if he were to devise a fake prom plan to make the girls' version look better and disguise his scam as a genuine proposal? Of course, there's no guarantee this delightfully devilish scheme will work, which is why Hachiman will need all the help he can get...