Each stat has its own icon that can be seen in an item's information area, or the overall total from all equipment can be seen when viewing each Hero.
The Attack stat shows how much damage per hit your Hero will deal to monsters as you fight. The attack icon is a small dagger that can be seen on Weapons items. To increase a Hero's attack, you can Fuse your weapons to increase their level or purchase stronger weapons from the Heroes Menu.
Defense is displayed by a blue shield icon and is tied to the shield you have equipped. This stat shows the amount of damage your hero can take from enemy monsters. To increase this, you can Fuse your shields to increase their level or purchase stronger shields from the Heroes Menu.
The Health stat, represented by a red heart, shows how much damage you can take before your Hero needs to Heal. Once this number reaches zero, your hero will be unable to fight for 60 minutes while they Heal. To increase this stat, Fuse your armor to increase the level or purchase stronger armor from the Heroes Menu.
Luck is a special stat that helps increase the chance your Hero will perform a critical hit on a monster. It is represented by a green four-leaf clover icon. Critical hits do much higher damage to a Monster than normal, helping to kill them faster.