Here are the choices you need to make in order to get this achievement :
*** Spoiler - click to reveal ***
--The first choice doesn't matter
DAY 1--------------------------------------------------------------------------------------
Do not reply
Run after him
Attempt to take the cutlet
--It doesn't matter if you take the keys or not
Keep silent
DAY 2--------------------------------------------------------------------------------------
Map: Go to the kitchen dinning hall and then anywhere you want
Go alone
Do not bet with Alisa
--Lose against Ulyana at the tournament
Map: Go to the scene
DAY 3--------------------------------------------------------------------------------------
Fine, wait a minute
You know, Olga asked me to help her tonight...
Who cares? I better keep on looking for answers
Fine, I'll help the sports club
Stay and help Ulyana with cleaning up
DAY 4--------------------------------------------------------------------------------------
Map: Go to the forest and then to the bus stop
Don't go with Miku
Just asking...
Got food poisoning from the canteen?
Ask about the bundle
Do not give Alisa the activated carbon
--It doesn't matter if you eat the apple or not
Go with Ulyana
--Choose any combination of directions
DAY 5--------------------------------------------------------------------------------------
Map: Go to the club house
Refuse
--It doesn't matter with who you go
Yep, I tried my best!
Map: Go the infirmary, to the club house and then to the library
Try to snatch the book out of Alisa's hand
Do nothing, just stay seated
Go to Ulyana
DAY 6--------------------------------------------------------------------------------------
Try to stop her verbally
DAY 7--------------------------------------------------------------------------------------
--For the good ending
That's all my fault!
--For the bad ending
That's all her fault!