Koschei's Troubles

You can start by first talking to Thorvald the Warrior in Rellekka. He will say that something is wrong with Koschei and he needs your help, and to go down the stairs to where you fought Koschei during The Fremennik Trials.

Koschei will ask you to go south of Rellekka to chop down a strange blossoming tree that he has seen. You will need the Balmung to do so. Chopping down the tree will reveal a Strange chest in the stump. Return to Koschei and he will unlock the chest revealing a toy ship. He will tell you to put the toy into the well in Rellekka. Doing that the toy will turn into a White jewel.

Return to Koschei and he will ask you to modify the jewel. You can:
 * cut the jewel turning it blue
 * Smash the gem with the Bulmung (requires 90 Strength), turning it red.
 * Check the gem for curses requires (90 Prayer).

When you modify the gem give it back to Koschei and he will turn into Kharshai. Kharshai will then upgrade the Bulmung for you. You have completed the miniqest.

Rewards

 * Antique lamp
 * Enhanced Balmung

If you have the levels you can go back to Kharshai and modify the gem again using the opitions you didn't use durning the miniquest. This will give Kharshai a new memory and will also turn your Bulmung the color of the gem.