Core Elm: 

• Location: Challenge > Core Elm
• Players can upgrade designated Element Heroes Power via Core Elm
• Using same Element SR Hero Shards and Rainbow Dew, Fortune Bonus Effect of Core Elm can be increased.

• Once each Fortune Bonus Effect is upgraded, Level of Core Elm will increase, increasing the maximum Fortune Bonus Effect Level.
  Each Fortune Bonus Effect Level cannot exceed 5 Levels over the closest Bonus
  For example, One Fortune Bonus Effect is at Level 5, another at Level 1, while the others are at Level 0, that Fortune Bonus Effect cannot be raised to Level 6 without first Leveling up the Level 1 Bonus.
• (Maximum Level cannot exceed Level of Core Elm

Note: Rainbow Dew can be obtained from daily quests.