You get it by completing the Dark of The Moon quest, which you can get from Lunar Master, and completing the Blaze of the Sun quest, which you can get from Sol.
Moon Quest: Lunar Master spawns during full moons, in a room behind the Soul Reaper arena at Haunted Castle. To accept the quest, you must be level 1700+
Dialogue:
1: Hello.
2: Nevermind.
1A: So, you have arrived at my home. I have a few errands I need you to do.
1B (not enough levels) You are too weak. Come back later.
C: Tell me, and I shall help.
D: Defeat 100 Living Skeletons.
Once you have defeated 100 living skeletons, he will tell you to go talk to the Death King npc. The Death King npc will give you a Dark Key, and once you have given the key to Lunar Master, he will reward you with the Crescent Moon Blade.
Sun Quest: Find Sol, who only spawns when the Sun is at the highest point in the sky, and despawns after 5 minutes.
He will ask you to find his brother, Ra, who spawns at the top of Hydra Island.
Once you have found Ra, he will tell you to fight him. He uses Awk Flame (New version) and has 5 instinct dodges. Once you have dealt 100k damage to him, he will tell you that you have bested him and he will give you a scroll. Give this scroll to Sol and he will thank you.
Z: Lunar Eclipse: Full Shade
The user stabs their blade into the ground. At the same time, a dark spear will stab the enemy, pinning them to the ground while releasing black smoke.
Dmg: 2.5k
CD: 15 seconds
M: 175
X: Solar Eclipse: Shining Glory
The user throws their blade into the air, creating a trail of flames that spreads out and flies at the enemy.
Dmg: 4k
CD: 20 seconds
M: 350
