Secretcalibur

Secretcalibur (ひみつかりばー, Himitsu-karibā) is the special Dual Blades-category unique skill, owned by Shioko Kirigaya. The prerequisites to use this skill is a Dual Blades skill level of at least 900 and two swords, Holy Sword Excalibur, obtained from the Holy Sword of the Ice Palace quest, and Demonic Sword Excalibur Morgan, obtained after clearing all quests within the Blackened Camelot Singularity.

Overview
The skill starts out similarly to Starburst Stream, performing the first ten hits of that skill. Leaping backwards, the user then performs an attack that is the exact same as the Cygnus Onslaught sword skill, ending the skill and dealing massive damage.

Trivia

 * The skill itself is a copy of Mysterious Heroine X's Noble Phantasm, Secretcalibur.
 * If you look closely at the image, you can see that it is taken from Fate/Grand Order.