Here is a guide on how to get true ending in the game.
Here’s what to do from Chapter 6 onwards:
1) Have all 5 Key Items before reaching Chapter 7.
2) You need Luji Plateau added to World Map (from Chirper in Chapter 5).
3) Luji Plateau contains Plan for Nekutoki Forest (required dungeon for True Ending).
4) You are on the right track, if Mr. Badd fights you in Chapter 8 right before Yellow Heart.
5) In Chapter 9, there are several events in Planeptune and Peashy joins. After this, a few ? events are in Planeptune and you have to fight Arfoire with Neptune.
6) Play Chapter 9 till Extradimensional Space is available (but do not clear the dungeon, aka do not view the event at the end).
7) You need 6 specific dungeons from plans:
- So Shal Forest (Plan in Hello Continent)
- Vida Dimension (Plan in Lastation)
- Keraga Dimension (Treasure from Nekutoki Forest)
- Pi Shii Game Factory (Treasure from Keraga Dimension)
- Powerlevel Island (from Planeptune after defeating Fake Purple Heart), 2nd area is called Leggo Island
- Graphic Pass (Eden after Extradimension Space is open)
8) Create the dungeons in this order: So Shal Forest + Keraga Dimension -> Pi Shii Game Factory -> Vida Dimension + Graphic Pass -> Powerlevel Island; View the events in the dungeons.
9) View event in Extradimensional Space.