This is the Training Tower. Kind of an imposing name, isn't it?
At the Training Tower, you can select and fight foes which match the attack ability of your Heroes. This is the best way to level up as fast as possible.
I see. Commander Anna, you must have entered the Training Tower countless times in order to gain experience!
Other ways to efficiently gain experience are the Special Training maps and upgrading your castle. Feel free to take a look, if you're interested!
(This is a lot to take on board all at once...)
Level Up Fast in the Training Tower!
At the Training Tower in the Battle Menu, you can try a Stratum appropriate to the level of your allies, from level 1 to 5 or 10 and onward! It doesn't use a lot of stamina to try the Training Tower. We recommend selecting foes that you can easily destroy. The map and combination of foes changes randomly each time that you try a Stratum. You can also change the map and combination of foes by tapping the green Refresh button next to the title toward the top of the screen.
Special Training for Tons of Experience
In Special Training maps, you want to match your team to a map based on their attack type. For example, there is a melee map and a ranged map. The maps change and reappear on a daily basis. Although Special Training is divided by level, it isn't divided in the same detail as the Training Tower. Also, foe reinforcements arrive in great numbers. This means that battles tend to be very long. Try selecting a low level and taking a staff-wielding Hero with you.
Upgrade Your Castle for Bonuses
In the Shop menu, you can spend Orbs to get upgrades for your castle. Once a castle type is unlocked, it provides a perpetual experience bonus. Unlocking the Royal Castle means you'll get double EXP! When you first start playing, we recommend prioritizing upgrading your castle.