Just be a waste of oxygen and skip the events mentioned in the Good Ending. One missed event is enough to lock you out of further Nep. No university will take you at this point. Just get a rope and end it. Everyone around you expects it.

All you need is to watch certain events in chapter 5 and 6.
Those events will give you the following items which are required for the Good Ending:

IFs Notebook (At the start of chapter 5 - Planetune)
Compas Syringe (At the start of chapter 5 - Planetune)
Neps Pudding (Chapter 5 after helping any nation - Planetune)*
Stuff Animal (Story progression)
Peashys Drawing (At the start of Chapter 6 - BLANETUNE)

*Pudding is missable if you are a miserable piece of filth that skips events.

How do you know that it worked?
Nep and Puru will say that they have a plan prepared before they set out to get Pea.

For the True Ending visit the events of the following dungeons but also get the Good Ending requirement done. The referred events are black&white flashbacks which are easy to spot. Each dungeon is in a different area. Also watch each and every event you come across. Be paranoid; Check all maps after every main event.

So Shal Forest (Chapter 9 - Chirper)
Keraga Dimension (Nekutoki Forest - Treasure)
Pii Shii Game Factory (Kerage - Treasure)
Graphic Pass (Chapter 9 - Chirper)
Vida Dimension (Chapter 9 - Chirper)
Powerlevel Island (Chapter 9 - Chirper)

Did it work?
It worked when your whole Neparty went over to the other side.