Inseparable Sword is a Greatsword in Elden Ring. The Inseparable Sword scales primarily with Strength, Dexterity and Faith and is a good Weapon for Faith Builds. 

Elden Ring Inseparable Sword Notes & Tips

• Weapon Skill: Sacred Blade
• This weapon cannot be infused with Ashes of War
• Can't be enchanted with Magic nor boosted with Consumables.
• Inseparable Sword can be upgraded by using Somber Smithing Stones
• This weapon, alongside the Banished Knight's Greatsword and Knight's Greatsword features an alternate Greatsword moveset with unique two-handed R1 attacks. This moveset is drawn from Dark Souls 2's Mirrah Greatsword and Dark Souls 3's Hollowslayer Greatsword. 
• The Inseparable Sword is the only greatsword that is placed on the hip when sheathed.
• Deals +20% damage to  Undead type enemies and prevents Skeletons from reviving
• At 80 Faith has the highest Attack Rating of all Holy Damage dealing Greatswords, if you have not invested in Strength or Dexterity much.
• Sell Value:   200
• NOTE: As of Patch 1.09, the scaling values of this weapon were changed. Please refer to the Upgrades Table of this weapon below. Additionally, speed, range, recovery time and guard counter speed of Greatswords weapons has increased.