How do you Equip Runes?

In Soul Seeker: Six Knights there are 135 runes which are then divided into four different types. These are attack runes, defense runes, magic runes, and special skill runes. Runes also come in three quality levels - low class (green), middle class (green), and high class (blue). Runes are obtained by playing the Dungeons of Demon mode, as a reward, by summoning.

You can combine runes to upgrade them and the number you can equip a hero will depend on their level. However, runes cannot be equipped to any hero, you have to equip the right rune to a matching hero. For example, you will only be able to equip the defense type rune to guardians and the magic type rune to wizards.