Damage increases your character's damage per hit. Armor decreases the damage received from enemies. Whenever a character moves, it will receive damage automatically from nearby enemies. However, if you don't move, you will still receive damage for every 1 second from nearby enemies. So increasing your armor will absolutely help you stay more longer and receive less damage when you are moving. Moving at any directions will automatically draw your sword in that direction also. It will deal damage to the nearby enemies. If the enemy doesn't die when you move/attack at his direction, you will stay in that location and the next time you move again, you will still receive damage from the same enemy. Damage will help you kill enemies at fast rate. You can also travel or move a lot if you have high damage because you can kill enemies at 1 hit or fewer hits. Since you can move a lot faster, getting gems is more easier than having a high armor status attribute.
The only advantage of having a high armor is you can travel a lot further compared to having high damage. Travelling further will give you an opportunity to farm or get higher class gems.
However, you don't need higher class gems because they can only be used at higher upgrades also.
You will still eventually getting higher class gems with high damage because when you have high damage, the required gems for "damage" will upgrade to higher class gems also. Assuming if you have a higher upgrades of damage and lower upgrades of armor, you can easily upgrade your "armor" because it only requires lower class gems and it is very easy to get that with having high damage attribute. Since you can get lower class gems easily with high damage, you can easily upgrade other skills and items that will absolutely help you in getting more gems.
The Secret Tower becomes available when you complete the 10th floor of the Area. Each Area has it's own secret tower. You can get double character & Gems if you successfully complete the Secret Tower. However, the secret tower costs more stamina than other floors. The battle preparation screen for the same tower is same as that of other towers.
Link can be activated between heroes from other characters. Celestial Love: Characters will get bonus status when "Link: Friend" relationship is activated. Celestial Hatred.: Players will get positive or negative bonus when "Link: Enemy" relationship is activated.