These are some secrets in the game, most of them of course are true ending content.
1. Do not bother buing premium points in this game. During normal gameplay we will get plenty of them. Also, the Battle Arena rewards mostly the AMP points. The Bronze-Hard cup rewards some Battle Points, and the Silver cup onwards rewards 2, 3 and 4 AMP points respectively. The most tiring and stupid is the Gold-Hard cup because we to have to fight with the Virus active... From the other hand, the Maid-Hard Cup is so easy that You can beat it with auto battle.
2. It seems there isn't a Secret Arena in this game. Instead, we have to fight Maidame Curie. Currently she keeps killing me, so I don't know whether she's the only combatant, or there are more after her.
3. Speaking of her, she doesn't appear in this game almost at all. Jolie yes, she is at the Battle Arena, and gives us a boat. Maidame Curie appears almost at the very-very end of the game, and in the post game.
4. And she gives us the flying vehicle. Yes, in one of the worlds (among four in total) we get the flying vehicle after beating the game. And in one of them (the water world) we don't get anything at all. Also....... I BET You gonna dislike it xDD
5. In this game the Clone Barrels game also exists:
He also can summon the final boss of the game... xD:
6. Some of the areas from the Asdivine Dios reappear. For example the Forgotten Village (obiously), but also for example the Ventus (AFAIR) stage. To enter this "Ventus stage" we have to pay some hard cash. I don't recall right now how much, but trust me that it is not cheap. This is like a bonus area. Enemies here are pretty easy, and there are several bosses. The first battle is with the Siblings Duo:
I have to say that I don't like them. Well, that girl at least. During the normal game when I had to fight her, I always decreased the difficulty level, because she at the start of the game used a very nasty attack that literally violated my characters. Upon killing them, we get 5 Life Seeds (+10 to HP and MP). We then can attack them again. Worth mentioning that their surname is Glory. 
The second battle is with Maids. Four of them. At once:
Upon killing them we get Ability Seed (+5 to all attributes), and an object. We then can challenge them again.
The object we received allows us to open a door to a third, and final battle. This time with Joile's "sisters":
Upon killing them we get an EXP Ring (increases the XP received, but it is not mentioned how much). I didn't try to attack them again, so I don't know if they will keep giving it, or it was just a single opportunity.
Then at the summit there are some treasure chests, but believe me that there is nothing interesting in them.
7. The Gazillion Challenge is in here as well. This time we fight against Maidame Curie. It seems it has two rewards. The first time I received 5 AMP points. But the damage I dealt was rather small (I think it was ~10 million):
As the spoiler title tells, this then appears after Maidame will show us how much she's happy and asks us to post that at the Twitter. It changes though, because when for the second time I fought (and this time I dealt some serious damage), the pop-up changed slightly:
Perhaps it is a good time to show my results...
and 999 hits. Since I have reached attachments limit, I will post that in the subsequent message.
2. It seems there isn't a Secret Arena in this game. Instead, we have to fight Maidame Curie. Currently she keeps killing me, so I don't know whether she's the only combatant, or there are more after her.
3. Speaking of her, she doesn't appear in this game almost at all. Jolie yes, she is at the Battle Arena, and gives us a boat. Maidame Curie appears almost at the very-very end of the game, and in the post game.
4. And she gives us the flying vehicle. Yes, in one of the worlds (among four in total) we get the flying vehicle after beating the game. And in one of them (the water world) we don't get anything at all. Also....... I BET You gonna dislike it xDD
5. In this game the Clone Barrels game also exists:
[img img=53]2015_12_06_17.37.52.jpg[/img]
[img img=54]2015_12_06_17.38.41.jpg[/img]
[img img=55]2015_12_06_13.50.31.jpg[/img]

The second battle is with Maids. Four of them. At once:
[img img=56]2015_12_06_15.26.04.jpg[/img]
The object we received allows us to open a door to a third, and final battle. This time with Joile's "sisters":
[img img=57]2015_12_06_15.56.29.jpg[/img]
Then at the summit there are some treasure chests, but believe me that there is nothing interesting in them.
7. The Gazillion Challenge is in here as well. This time we fight against Maidame Curie. It seems it has two rewards. The first time I received 5 AMP points. But the damage I dealt was rather small (I think it was ~10 million):
[img img=58]2015_12_06_16.41.31.jpg[/img]
[img img=59]2015_12_06_18.00.25.jpg[/img]
[img img=60]2015_12_06_17.58.48.jpg[/img]