Might is a basic measure of a Hero's current strength. Might isn't directly indicative of the usefulness of a Hero, but rather a measure of it's development. Might is calculated through Hero level, Rarity, Soulbinds, and the current level of Reborn.
The tables below show the affect of Levels, Rarity, Soulbinds, and Reborn on Might. Script error: The function "mighttables" does not exist.