Shadow☆Star: First Form - Chain of Blackness (影☆星・壱ノ型［鏈黒］Kage☆Boshi: Ichi no Kata "Rengoku" in Japanese) is an enhanced form of Tsubaki's Chain Scythe form achieved after unlocking the full power of the Uncanny Sword.
While using Shadow☆Star, Black Star commences a Soul Resonance with Tsubaki. The Soul Resonance draws Black Star's shadow towards the blade, and transmutes the sword into a long black sharp sickle-blade, with white ornante patterns on it with a handle attached for the wielder, accentuated with three short spikes. A long black chain, composed completely out of Black Star's shadow, circles Black Star twice before it ends at the ground where his shadow is.
The blade on the Chain of Blackness is long enough to be wielded as a sword, due to its original form as a chain scythe, Black Star is capable of throwing it towards the opponent in the form of a long-range attack. Since the chain originates from Black Star's shadow, Black Star can still control the trajectory of the blade, even if its thrown a great distance away. There is always a part the chain that encircles Black Star wherever he is, giving him protection from assaults from all sides.
Black Star also refers to this form as the form of 'power,' arguable making the Chain of Blackness the superior form of Shadow☆Star in terms of attack. However, it lacks the speed and stealth of some of its other forms.
This form is first used in the final fight against Mifune. Although Black Star manages to slightly wound Mifune with Chain of Blackness, he quickly switches to another form when he finds that sheer power is not enough to counter Mifune's Infinite One-Sword Style.