Here is the full list of all 55 Summer Meetings achievements.
Started the game
Did you thought she'll appear again?
Went to the sea
Seen all 15 festival events!
Someone confessed their love at festival!
You broke up in style!
Admitted your disloyalty
Decided to break all bonds except one
Seen an ending
Went to a concert
Got back together with someone
You don't know what a promise is, do you?
You did not forget!
Faced two alternatives
Just... why?
She never had a chance
What did you think would happen?
You've been caught
Kissed at least four girls during a playthrough
Rejected a confession
After rejecting a confession, asked her on a date
Seen all epilogues
Decided to return, but changed your mind at the last second
You were just curious what happens, right?
Things are getting weird
Activated #Help in settings
Pushed someone away
Stuck with one girl from the start
Learned the reason of breakup
Parted in peace
Ran to someone but didn't speek
You thought it guaranteed a happy ending?
That's not how a festival should be...
Finished the game before it really started
Not nice, is it?
That's not good...
Lost a place to stay
Lost a place to stay TWICE
Four heroines met
A difficult situation turned a bit awkward
Visited the oceanarium
Learned something
Someone got scared of you
Got the worst ending
Started dating Reina
Started dating Shiori
Started dating Yuka
Started meeting with Mei
Started dating Akari
Will it lead somewhere?
Seen Reina's epilogue
Seen Shiori's epilogue
Seen Yuka's epilogue
Seen Mei's epilogue
Seen Akari's epilogue