The Sword Impulse Gundam SPEC II is an enhanced version of the ZGMF-X56S/β Sword Impulse Gundam, secretly modified by Erica Simmons at the request of Cagalli Yula Athha. The upgrade includes a significant boost in battery capacity, and the Variable Phase Shift Armor has undergone major changes, swapping much of the original white with red, including on the v-fin. Additionally, the chest and shoulders now sport a black color scheme. Despite these changes, the Sword Impulse SPEC II retains all of the original's combat capabilities.

• Type 35 Prototype Advanced Railgun
• Sword Silhouette
• High Energy Beam Rifle
• Mobile Shield
• Folding Razor Anti-Armor Knife ×2
• Silhouette Flyer
• Core Splendor Parts Set
• Hand Parts Set
• Joint Parts

This upgraded model was one of three mobile suits modified by Erica Simmons at a covert Orb Union asteroid base to reinforce Compass' forces in case of an emergency. This foresight proved valuable when the crew of the LHM-BB03S Millennium needed new mobile suits after suffering losses during the Eldore incident. The suits were crucial for their plan to rescue Lacus Clyne from the Kingdom of Foundation, who had concealed her within the space fortress Artemis.

Piloted by Lunamaria Hawke, the Sword Impulse SPEC II was deployed to protect the Millennium as it cleared a path toward the Requiem superweapon. After using up the weapons on the Blast Impulse SPEC II, Lunamaria switched to the Sword Silhouette to continue the fight. During a fierce duel with Agnes Giebenrath's GYAN Strom, which had defected to the Foundation, the Sword Impulse lost all its close combat weapons when Lunamaria hurled them at the enemy suit. With its power drained, the Sword Impulse transitioned to the Force Silhouette, recharging via the Destiny's Deuterion Beam Energy Transfer System, allowing the battle to continue.