You can get basic information about this system on official page (HERE).

Legacy of Heavenly King can be bought at NPC in Narootuh (Handworker of Heaven King) for 50 Gold Coins. You will have basic stats (atk/mag atk 9-11 and 2000 HP) and all slots will be locked - you can unlock them with upgrading Legacy of Heavenly King (every new Tier).

When you unlock each slot you can place  Ancient Relics (gained from The Lawless zone of Dead person boss and the Infinity Tower boss) item on it and you will get random Relics stats (with random value) from table below:

STR (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
HEALTH (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
INT (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
WIS (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
AGI (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30)
HP (1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000)
DEF (30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50)
OTP (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
EVA (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
CRITICAL (1%, 2%, 3%, 4%, 5%)
CRITICAL DMG (1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%)
EXPLOSIVE BLOW (1%, 2%, 3%, 4%, 5%)
EXPLOSIVE BLOW DMG (1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%)
PVP ATK/DEF (2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
ALL RESIST (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
WATER ATK + DEF (2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
WIND ATK + DEF (2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
LAND ATK + DEF (2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
ATK (10 - 20, 11 - 21, 12 - 22, 13 - 23, 14 - 24, 15 - 25, 16 - 26, 17 - 27, 18 - 28, 19 - 29, 20 - 30)
MAG ATK (10 - 20, 11 - 21, 12 - 22, 13 - 23, 14 - 24, 15 - 25, 16 - 26, 17 - 27, 18 - 28, 19 - 29, 20 - 30)

When you upgrade Legacy of Heavenly King you also get increased Attack/Magical attack and HP every level:

Tier 1 (Alpha), Level 1 - Attack/Magical attack: 9 - 11 and HP: 2000
Tier 1 (Alpha), Level 2 - Attack/Magical attack: 10 - 13 and HP: 2150
Tier 1 (Alpha), Level 3 - Attack/Magical attack: 11 - 14 and HP: 2300
Tier 1 (Alpha), Level 4 - Attack/Magical attack: 12 - 15 and HP: 2450
Tier 1 (Alpha), Level 5 - Attack/Magical attack: 13 - 16 and HP: 2600
Tier 1 (Alpha), Level 6 - Attack/Magical attack: 14 - 17 and HP: 2750
Tier 1 (Alpha), Level 7 - Attack/Magical attack: 15 - 18 and HP: 2900
Tier 1 (Alpha), Level 8 - Attack/Magical attack: 16 - 19 and HP: 3050
Tier 1 (Alpha), Level 9 - Attack/Magical attack: 17 - 20 and HP: 3200

Tier 2 (Beta), Level 1 - Attack/Magical attack: 18 - 21 and HP: 3350
Tier 2 (Beta), Level 2 - Attack/Magical attack: 23 - 28 and HP: 3500
Tier 2 (Beta), Level 3 - Attack/Magical attack: 24 - 29 and HP: 3650
Tier 2 (Beta), Level 4 - Attack/Magical attack: 25 - 30 and HP: 3800
Tier 2 (Beta), Level 5 - Attack/Magical attack: 26 - 31 and HP: 3950
Tier 2 (Beta), Level 6 - Attack/Magical attack: 27 - 32 and HP: 4100
Tier 2 (Beta), Level 7 - Attack/Magical attack: 27 - 33 and HP: 4250
Tier 2 (Beta), Level 8 - Attack/Magical attack: 28 - 35 and HP: 4400
Tier 2 (Beta), Level 9 - Attack/Magical attack: 29 - 36 and HP: 4550
Tier 2 (Beta), Level 10 - Attack/Magical attack: 30 - 37 and HP: 4700

Tier 3 (Delta), Level 1 - Attack/Magical attack: 31 - 38 and HP: 4850
Tier 3 (Delta), Level 2 - Attack/Magical attack: 36 - 44 and HP: 5000
Tier 3 (Delta), Level 3 - Attack/Magical attack: 37 - 46 and HP: 5150
Tier 3 (Delta), Level 4 - Attack/Magical attack: 38 - 47 and HP: 5300
Tier 3 (Delta), Level 5 - Attack/Magical attack: 39 - 48 and HP: 5450
Tier 3 (Delta), Level 6 - Attack/Magical attack: 40 - 49 and HP: 5600
Tier 3 (Delta), Level 7 - Attack/Magical attack: 41 - 50 and HP: 5750
Tier 3 (Delta), Level 8 - Attack/Magical attack: 42 - 51 and HP: 5900
Tier 3 (Delta), Level 9 - Attack/Magical attack: 43 - 52 and HP: 6050
Tier 3 (Delta), Level 10 - Attack/Magical attack: 44 - 53 and HP: 6200

Tier 4 (Epsilon), Level 1 - Attack/Magical attack: 45 - 54 and HP: 6350
Tier 4 (Epsilon), Level 2 - Attack/Magical attack: 50 - 61 and HP: 6500
Tier 4 (Epsilon), Level 3 - Attack/Magical attack: 51 - 62 and HP: 6650
Tier 4 (Epsilon), Level 4 - Attack/Magical attack: 52 - 63 and HP: 6800
Tier 4 (Epsilon), Level 5 - Attack/Magical attack: 53 - 64 and HP: 6950
Tier 4 (Epsilon), Level 6 - Attack/Magical attack: 54 - 65 and HP: 7100
Tier 4 (Epsilon), Level 7 - Attack/Magical attack: 54 - 66 and HP: 7250
Tier 4 (Epsilon), Level 8 - Attack/Magical attack: 55 - 68 and HP: 7400
Tier 4 (Epsilon), Level 9 - Attack/Magical attack: 56 - 69 and HP: 7550
Tier 4 (Epsilon), Level 10 - Attack/Magical attack: 57 - 70 and HP: 7700

Tier 5 (Zeta), Level 1 - Attack/Magical attack: 58 - 71 and HP: 7850
Tier 5 (Zeta), Level 2 - Attack/Magical attack: 63 - 77 and HP: 8000
Tier 5 (Zeta), Level 3 - Attack/Magical attack: 64 - 79 and HP: 8150
Tier 5 (Zeta), Level 4 - Attack/Magical attack: 65 - 80 and HP: 8300
Tier 5 (Zeta), Level 5 - Attack/Magical attack: 66 - 81 and HP: 8450
Tier 5 (Zeta), Level 6 - Attack/Magical attack: 67 - 82 and HP: 8600
Tier 5 (Zeta), Level 7 - Attack/Magical attack: 68 - 83 and HP: 8750
Tier 5 (Zeta), Level 8 - Attack/Magical attack: 69 - 84 and HP: 8900
Tier 5 (Zeta), Level 9 - Attack/Magical attack: 70 - 85 and HP: 9050
Tier 5 (Zeta), Level 10 - Attack/Magical attack: 71 - 86 and HP: 9200

Tier 6 (Eta), Level 1 - Attack/Magical attack: 72 - 87 and HP: 9350
Tier 6 (Eta), Level 2 - Attack/Magical attack: 77 - 94 and HP: 9500
Tier 6 (Eta), Level 3 - Attack/Magical attack: 78 - 95 and HP: 9650
Tier 6 (Eta), Level 4 - Attack/Magical attack: 79 - 96 and HP: 9800
Tier 6 (Eta), Level 5 - Attack/Magical attack: 80 - 97 and HP: 9950
Tier 6 (Eta), Level 6 - Attack/Magical attack: 81 - 98 and HP: 10100
Tier 6 (Eta), Level 7 - Attack/Magical attack: 81 - 99 and HP: 10250
Tier 6 (Eta), Level 8 - Attack/Magical attack: 82 - 101 and HP: 10400
Tier 6 (Eta), Level 9 - Attack/Magical attack: 83 - 102 and HP: 10550
Tier 6 (Eta), Level 10 - Attack/Magical attack: 84 - 103 and HP: 10700

Tier 7 (Theta), Level 1 - Attack/Magical attack: 85 - 104 and HP: 10850
Tier 7 (Theta), Level 2 - Attack/Magical attack: 90 - 110 and HP: 11000
Tier 7 (Theta), Level 3 - Attack/Magical attack: 95 - 116 and HP: 11150
Tier 7 (Theta), Level 4 - Attack/Magical attack: 99 - 121 and HP: 11300
Tier 7 (Theta), Level 5 - Attack/Magical attack: 104 - 127 and HP: 11450
Tier 7 (Theta), Level 6 - Attack/Magical attack: 108 - 132 and HP: 11600
Tier 7 (Theta), Level 7 - Attack/Magical attack: 113 - 138 and HP: 11750
Tier 7 (Theta), Level 8 - Attack/Magical attack: 117 - 143 and HP: 11900
Tier 7 (Theta), Level 9 - Attack/Magical attack: 122 - 149 and HP: 12050
Tier 7 (Theta), Level 10 - Attack/Magical attack: 126 - 154 and HP: 12200
Legacy of Heavenly King Completed - Attack/Magical attack: 131 - 160 and HP: 12350

You need Spirit of Gwa-bo (Resting place of Dead Person and The Lawless zone of Dead person), Spirit of Hyeong-yo (gained in Infinity tower - D7), Spirit of Chi-woo (gained in Tower of D'ewah - D6), Heavenly treasure (gained from The Lawless zone of Dead person boss and the Infinity Tower boss) and Gold Coins (gained from KC boxes, Dewah Shadow, etc...) to upgrade each Level and Tier:

You can also get all Spirit items at Handworker of Heaven King NPC as daily mission (10 oieces of each item for 1 gold coin every day). Second option to get Spirit items and Heavenly treasure item is in Legacy of Heavenly King Box (limited time sale).

Tier 1 (Alpha), Level 1:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 2:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 3:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 4:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 5:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 6:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 7:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 8:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 1 (Alpha), Level 9:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1


Tier 2 (Beta), Level 1:
Spirit of Gwa-bo: 10
Spirit of Hyeong-yo: 10
Spirit of Chi-woo: 10
Gold Coins: 1

Tier 2 (Beta), Level 2:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 3:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 4:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 5:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 6:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Heavenly treasure: 1

Tier 2 (Beta), Level 7:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 8:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 9:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10

Tier 2 (Beta), Level 10:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Gold Coins: 10


Tier 3 (Delta), Level 1:
Spirit of Gwa-bo: 20
Spirit of Hyeong-yo: 20
Spirit of Chi-woo: 20
Heavenly treasure: 1

Tier 3 (Delta), Level 2:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 3:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 4:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 5:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 6:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Heavenly treasure: 2

Tier 3 (Delta), Level 7:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 8:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 9:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20

Tier 3 (Delta), Level 10:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Gold Coins: 20


Tier 4 (Epsilon), Level 1:
Spirit of Gwa-bo: 50
Spirit of Hyeong-yo: 50
Spirit of Chi-woo: 50
Heavenly treasure: 2

Tier 4 (Epsilon), Level 2:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 3:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 4:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 5:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 6:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Heavenly treasure: 20

Tier 4 (Epsilon), Level 7:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 8:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 9:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40

Tier 4 (Epsilon), Level 10:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Gold Coins: 40


Tier 5 (Zeta), Level 1:
Spirit of Gwa-bo: 300
Spirit of Hyeong-yo: 300
Spirit of Chi-woo: 300
Heavenly treasure: 20

Tier 5 (Zeta), Level 2:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 3:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 4:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 5:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 6:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Heavenly treasure: 50

Tier 5 (Zeta), Level 7:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 8:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 9:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60

Tier 5 (Zeta), Level 10:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Gold Coins: 60


Tier 6 (Eta), Level 1:
Spirit of Gwa-bo: 500
Spirit of Hyeong-yo: 500
Spirit of Chi-woo: 500
Heavenly treasure: 50

Tier 6 (Eta), Level 2:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 3:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 4:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 5:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 6:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Heavenly treasure: 100

Tier 6 (Eta), Level 7:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 8:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 9:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100

Tier 6 (Eta), Level 10:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Gold Coins: 100


Tier 7 (Theta), Level 1:
Spirit of Gwa-bo: 1000
Spirit of Hyeong-yo: 1000
Spirit of Chi-woo: 1000
Heavenly treasure: 100

Tier 7 (Theta), Level 2:
Spirit of Gwa-bo: 2000
Spirit of Hyeong-yo: 2000
Spirit of Chi-woo: 2000
Heavenly treasure: 100

Tier 7 (Theta), Level 3:
Spirit of Gwa-bo: 2100
Spirit of Hyeong-yo: 2100
Spirit of Chi-woo: 2100
Heavenly treasure: 110

Tier 7 (Theta), Level 4:
Spirit of Gwa-bo: 2200
Spirit of Hyeong-yo: 2200
Spirit of Chi-woo: 2200
Heavenly treasure: 120

Tier 7 (Theta), Level 5:
Spirit of Gwa-bo: 2300
Spirit of Hyeong-yo: 2300
Spirit of Chi-woo: 2300
Heavenly treasure: 130

Tier 7 (Theta), Level 6:
Spirit of Gwa-bo: 2400
Spirit of Hyeong-yo: 2400
Spirit of Chi-woo: 2400
Heavenly treasure: 140

Tier 7 (Theta), Level 7:
Spirit of Gwa-bo: 2500
Spirit of Hyeong-yo: 2500
Spirit of Chi-woo: 2500
Heavenly treasure: 150

Tier 7 (Theta), Level 8:
Spirit of Gwa-bo: 2600
Spirit of Hyeong-yo: 2600
Spirit of Chi-woo: 2600
Heavenly treasure: 160

Tier 7 (Theta), Level 9:
Spirit of Gwa-bo: 2700
Spirit of Hyeong-yo: 2700
Spirit of Chi-woo: 2700
Heavenly treasure: 170

Tier 7 (Theta), Level 10:
Spirit of Gwa-bo: 2800
Spirit of Hyeong-yo: 2800
Spirit of Chi-woo: 2800
Heavenly treasure: 200