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It is a unique one-on-one party system which can only be found in Asda Story.
Additional EXP can be gained apart from a general party system.
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1.  Right click on the character you wish to form a soulmate with and select Request Soulmate. A message will be sent to the other player letting them know that you wish to become Soul Mates with them.
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2.  You can also send soul mate request messages to other users through the Soul Statue NPC in Alpen town.
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Soulmates are formed between accounts.

In other words, even though you have chosen a specific person to Soul Mate with, you are also Soul Mated with all of their other Alts in that same account.
3. Once the other player accepts the request, you will be Soul Mated with them.
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4. Once a soul mate is formed, a loop of soul will appear.
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1. Meet Cave in the northwest part of Alpen town in order to cancel the soulmate.
Cancelling the soul mate can be done at any time by either player.
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Tip.  There is no penalty to cancel the soulmate, but the record will remain.
A total of 3 previous soulmates will remain in record, and if you had more than 3 soulmates, old records will be deleted in order. If you wish to re-form with an old Soul Mate, you will start back at level one.
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1.  Soulmate Info Window (Shortkey U)
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2.  Soulmate Skills
[ As the level of soul mate goes up, more and more Soul Mate skills become available. ]
Icon Skill Name Recharge time Description
Soulmate icon01 Delivery of Soulbody 12 Hours When logging out after activating the skill, your Soul body will be delivered to your soul mate. This Soul body can gain certain amount of EXP off of the soul mate. These points can be used when you log back in.
Soulmate icon02 Summon of Soulmate 20 Min Summon your soul mate to your area. It allows you to easily meet your soul mate at any place.
Soulmate icon03 Protection of Soul 20 Min This skill allows you to protect the soul of your soul mate to avoid the death penalty which reduces 10% of EXP.
Soulmate icon04 Whisper of Resurrection 10 Min It immediately resurrects the soul mate from death.
Soulmate icon05 Move of Soulmate 20 Min Move yourself to where your soulmate is. It works between different channels or maps.
Soulmate icon06 Power-Up Passive(none) When your soulmate is around, you can increase attack power by 10% through spiritual interaction.
Soulmate icon07 Healing of Soul 15 Sec *Recover 80% of physical power of your soulmate.

*It works between different levels since it's based on the percentage.

Soulmate icon08 Combination of Soul 60 Sec *Borrow 70% attack from your soulmate.

*Disregarding the level difference, you can use 70% of your soulmate's attack power for hunting.

Soulmate icon09 Song of Soulmate 12 Hours All stats increase 50% for 30 minutes.
Tip. Combination of soul skill is useful when the soulmate is formed between high and low levels, it enables soul mates attack together, by letting low level to borrow high level's attack(or magic) power.
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Delivery of Soulbody is to leave your soul body with to your soul mate before logging out, so when you come back, part of your soulmate's EXP will be given to you as a gift.
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Tip.  When the figure in the Soulbody info reaches 100%, no more EXP can be gained. However, more EXP can be saved when using higher level Soulstones
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If two soulmates catch monsters when they are close to each other, a soulmate apple appears to save part of monsters' EXP. The apple will grow as soulmates continue to hunt, and eventually turn into a golden apple after 100 kills, which can be eaten for an EXP bonus. The higher level of monsters killed when "growing" the apple, the more bonus exp you receive when you eat the resulting golden apple.
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Tip.  Mouse over the apple to check the accumulated EXP.
Tip.  Killing 0-EXP quest items will each count as 1 kill toward the total, as will bosses, so apples can hold very different amounts of experience.

Note: When you are with your soul mate, your exp will count twice, even if you are not in a party. Simply kill a monster with your partner nearby and you will get the exp you would if they were in a party with you, as well you will get the equivalent of their exp. So say one soul mate is level 20 and the other is 15, where the level 20 gets 100 exp, the level 15 might get 70 for having a higher level if they were in a party, as soul mates they each get a pay of 170 exp for it.