To proceed with this quest, you have to be minimum rein 10 (Lv 109) and already finished 'Found the Path to Mount Haku' quest (because you will need to get the item from rift boss).

If you have already done all of it, the 1st step you need to do is defeat rift bosses until you get the hearts.

Warrior will need Heart of Ma,
Mage will need Heart of Rang,
Poet will need Heart of Kyum, and
Rogue will need Heart of Chun.

Bring the heart to Trowulan Palace, and go to the library. In the library go to the secret room (009,004).

With the heart in your inventory find the book of 'Secret of Yong Weapon'. It will appear randomly (not always in the same spot!) so be patient. Press "o" while facing the bookshelves to find the book!

Once you find the book, click to read, and it will ask you to bring 4 pieces of your job weapon from Lv 60-70-80-90-99.

Poet:
Lv60 Death Brain,
Lv70 Trident,
Lv80 Titan Spear,
Lv90 Charm Rod,
Lv99 Magic Charm Rod

Warrior:
Lv60 Maxcaliber,
Lv70 Goblin Bat,
Lv80 Electra,
Lv90 Spiky Bat,
Lv99 Spiky Cleaver

Mage:
Lv60 Sadistic Staff,
Lv70 Shocker Trident,
Lv80 Star Staff,
Lv90 Wave Rod,
Lv99 Magic Wave Rod

Rogue:
Lv60 Moon Blade,
Lv70 Soldier Fork,
Lv80 Spiky Dagger,
Lv90 Bloody Sickle,
Lv99 Bloody Cleaver

For the Lv99 weapon, you could ONLY get them from GIFTBOX!

Submit all those and it will ask you to bring your job 1st and 2nd tier from Sabana creation. It will ask for 2 pieces of each.

Poet:
1st tier Snow Spear,
2nd tier Gaia's Staff

Warrior:
1st tier Thunder Javelin,
2nd tier Gaia's Blade

Mage:
1st tier Magical Dragon Staff,
2nd tier Gaia's Orb

Rogue:
1st tier Set Stick,
2nd tier Gaia's Stiletto

Finally, it will ask for the last item, which is your Spirit Weapon Job (2 pieces).

After all that hustle, it will show you the recipe to create Yong Weapon.

Recipe for Yong Kyum (Poet):
1 Fan of Japan,
1 Mist Titan Spear,
1 Heart of Kyum

Recipe for Yong Ma (Warrior):
1 Tae Jon Cleaver,
1 Mist Electra,
1 Heart of Ma

Recipe for Yong Chun (Rogue):
1 Yo Jon Sword,
1 Mist Spiky Dagger,
1 Heart of Chun

Recipe for Yong Rang (Mage):
1 Fan of Japan,
1 Mist Star Staff,
1 Heart of Rang
*** Need further confirmation because no one try creating mage's weapon yet! ***

For mist weapons, you could ONLY get them either from Dowhar / Bjorn Box / Elite Mystery boxes.

During creation process, 1 Heart (basic success rate) gives you 30% success rate which mean adding more heart gives you bigger chance of success (adding 2 heart means your success rate is 60% and so on).

If the process failed, everything gone!

Then if you already succeed creating the weapon, and you want to create another, you have to repeat the quest again (asked Edric and he said that and I have not yet tried to directly do creation without retaking the quest)


Credit to 'Mimi Peri' Malfice!
Who helped to crack the quest and at the same time bombing the 1st successfuly created weapon! :)