Here is the full list of all 14 Summer Daze: Tilly's Tale achievements.
Toast to a strong friendship with Fritz at the Festival
Enjoy listening to the music and dancing with Sitari at the Festival
Choose to see rare sights with Mooella after the well done Festival
Ride through the skies with Kitty during the Festival
Win the prize with Rodrigo at the Festival
Bring a whole new level of competition with Max at the Festival
Breeze through the semester without paying attention to your studies and don't get any help for the Festival
Pass all your exams and throw the best festival in the same playthrough
Passed all of the Rogue Class exams
You went above and beyond to decorate for the Festival, and ensured there would be good food and entertainment
You've seen every characters' finale
Win a game of La Boomba
Use a Boom to explode the Pizza card
Nobody else came for Beach Day