You can try limit break on Promoted ★6 Heroes.

If you have sufficient Essence of Hero items for limit break, you can activate limit break on the hero at Cabin.

If you reach all stats full, your hero rarity will be increased.

Hero Rarity will be increased like this 'Normal' ▶ 'Immortal'  ▶ 'Legendary'  ▶ 'Mythical' ▶ 'Mythical R'  

 ※ When you activate limit break on a hero, the hero's rarity can be increased at once at a low chance. 

 ※ According to hero rarity, the hero's frame and title will be changed. 

※ Last Updated on November 30th UTC.