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…

Volume 18 of the My Youth Romantic Comedy Is Wrong, As I Expected @ comic manga series by Wataru Watari.