Don't know if it's a little too late for that, but here is a walkthrough.
It's pretty straightforward, so you only need 2 saves.
Here are the choices and where to save then:
The choices may be a little different, since I'm translating from the Japanese.
----
-I understand
-I understand
-I understand
-Take the test
-Ask for cooperation
-(Save here - 1)
-Endure and go to school
-(Save here - 2)
There should be 3 options here, Just do one and Load Save 2, until the 3 are done.
-...Anzu... (End 1)
-...Takafumi... (End 2)
-...Mariko... (End 3)
After viewing the 3 endings, you will unlock the true end.
-Load Save 1
-Endure and go to school
A fourth option should appear here:
-Not enough...
After that, there should be an EXTRA section on the title screen, with a small story.
That's it. Hope it helps someone.