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