At player level 15 the feature Hero Promotion is unlocked. Every hero has several passive upgrades available that can augment their own stats or augment their skill. These upgrades can be found on the right side of the hero once you select them from your hero list on the left. Every promotion rank will unlock or improve 1 of the 5 upgrades that are available. Which rank is needed to improve or unlock this upgrade can be seen when hovering over it with your mouse.

To improve the rank of Hero Promotion you need a certain amount of Promotion Sapphires and specific Hero Cards. Promotion Sapphires are earned through daily activity chest rewards and events. Hero Cards can be earned through Valhalla when using Summon, combine Hero Shards when you have reached the required number or through the Heroic Soul Shop found at Valhalla. Some Hero Cards can also be earned through certain events. When you own the required Promotion Sapphires and the required Hero Cards the numbers will light up in white and you can click the Promotion button to improve the Hero Promotion rank by 1.

This guide is sourced from yabusame.