You need to gather all 7 jewels to see this true ending (the location covered on the guide below). Beat the game once (you can’t get true ending on the first playthrough). Load your clear data, and talk to Joule until she gives you a “handmade pendant”. Equip the pendant (via gear menu) and DON’T REMOVE IT. Now go to the last stage (Firmament) and beat the last boss (it will be quite hard since prevasion is disabled). Defeat the extra boss then TRUE ENDING :).
Change of area indicated by a loading screen!! (After destroying hexagonal barrier)
At the beginning of the area 2, continue until you see a conveyor belt like shown on the screenshot above. Use your flashfield and keep going to the right. You will see the jewel at the end of the path.
Continue until you reach a dead end (a dialogue). You will arrive at the spiky area, you will see it soon.
It’s locked by a red laser and there is a switch nearby, but if you can’t find the red switch nearby then simply continue until you reach the area with 3 lamps. Light the room and then backtrack (it’s not far from there).
It’s located at the end of the area 2. Descend using your flashfield, it’s located below the hexagonal barrier.
After defeating the mini boss on area 2 (alarm bell on conveyor belt with a lava pit), continue and you will see many boxes like on the screenshot below.
Destroy 3 boxes on the picture (make sure you don’t touch the red boxes accidentally). It will become like screenshot shown on the picture below.
Destroy those marked boxes and you will see 2 red boxes. Destroy them and you will be left with one grax box, destory it and then you can grab the jewel.
You need to climb up the tower to avoid water, it’s located behind one of its robot (start paying attention after passing the area with shutter door).
It’s located on the top of the alarm bell mini boss (see the screenshot). You need to have air hop ability to reach the jewel.