In his awakened form, Kaku has a black cloud surrounding his neck and body.

Source: https://gamerant.com/one-piece-just-revealed-a-new-member-of-the-rocks-pirates/

Luffy toyed with Lucci while Zoro held his own against Kaku very well.

Source: https://gamerant.com/one-piece-straw-hat-cp0-alliance-explained/

Seeking help from Luffy, Vegapunk took cover from the World Government officials and this led to Luffy and Zoro clashing against Lucci and Kaku respectively.

Source: https://gamerant.com/one-piece-straw-hat-cp0-alliance-explained/

So, assuming for a moment quantum dreams do become a reality: is it responsible to accentuate the positive, as Kaku does?

Source: https://www.theguardian.com/books/2023/apr/22/physicist-michio-kaku-we-could-unravel-the-secrets-of-the-universe

While Kaku was engaged in fierce combat with Zoro and holding his own against him, Stussy managed to sneak up on him easily and bite him in the neck, causing him to fall asleep immediately afterwards.

Source: https://gamerant.com/one-piece-how-strong-is-stussy/

Zoro admitted that he had never seen Kaku use this form prior to their current fight, which removes any possible doubts about it being the assassin's devil fruit awakening.

Source: https://gamerant.com/one-piece-just-revealed-a-new-member-of-the-rocks-pirates/