These greatsword variations of sunblades were created and used by the Lightwatch in the first era. After their disappearance, they fell out of use until the re-emergence of the Ballista in the third era.
Ballista Libra used two of these greatswords at once, and Ballista Gemini came into possession of one as well during the events of the The Light of Lunaria.
Weapon (greatsword), martial melee weapon, 2d6 slashing damage, two-handed, heavy, mastery: graze, very rare (requires attunement)
Appearing as an intricate hilt made out of the metal Arkaan, those wielding it can use a bonus action to cause a large sword of pure radiance to spring into existence, or make the sword disappear. It's construction and mechanisms feel similar to a traditional sun blade, but the size of the weapon is much larger and the light is given a hard edge.
You gain a +2 bonus to attack and damage rolls made using the weapon. On a hit, the weapon deals an extra 2d6 radiant damage.
Hamablade. As an action, you extend the sword and slice it in a 30-foot cone of pure light. Each creature in that area must make a DC 16 Dexterity saving throw, taking 8d6 radiant damage on a failed save, or half as much damage on a successful one. Once this action is used, it can't be used again until the next dawn.
Supreme Light. While you are attuned to this sword, any radiant damage that you do with or without this weapon bypasses resistance to radiant damage. You treat immunity to radiant damage as resistance instead.
Mastery: Graze. If your attack roll with this weapon misses a creature, you can deal damage to that creature equal to the ability modifier you used to make the attack roll. This damage is the same type dealt by the weapon, and the damage can be increased only by increasing the ability modifier.