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