#evil bubble

Throughout the series, Bubble has needled, questioned, and made comments about Caine, to Caine. In ep. 8, this is especially prevalent when Bubble starts to poke at Caine's insecurities. He even goes so far to call Caine broken and defective, among other insults, wrapping up with "Maybe you deserved to be abandoned...you really were the lesser of the two" as Caine is popping clones Bubble made of himself.

This isn't something a creation would do, especially to its creator, and it shows in Caine's reactions. Caine isn't stupid, but he is deeply insecure and appears to be at least partially sentient. As such, he can likely process emotions to some degree, leading to feelings of inferiority and displeasure in his work, and anger at the other characters for not enjoying his efforts. Bubble seems to know this, and use it to his advantage. His words in ep. 8, as well as his near-indifference in previous episodes, hint at a malevolent thought process aimed at Caine, that Caine would never allow or tolerate from something he created.

Bubble is clearly lesser in power to Caine, but he isn't controlled by Caine in the same way Pomni & Co., any NPCs like Gummigoo, or the circus itself are. He seems to exist on his own terms, unlike the rest of the cast. However, he is inextricably linked to Caine, as evidenced by the tongue bit in ep. 4, Bubble's first appearance in the pilot out of Caine's hat, and how Bubble is almost always seen in conjunction with Caine.

This also aligns with the theory of Bubble being the still-somewhat-autonomous second AI. If Caine is a first-generation AI and already at his level of power, the second AI would likely have even more power. If the second AI is Bubble, it would explain why Bubble is undermining Caine's self-control for his revenge, and why Bubble is able to insult Caine without Caine being able to completely stop him, as seen in the Bubble-popping in ep. 8. In addition, Caine knows better than to create something like Bubble: rude, insulting, and ultimately unhelpful in the final goal. Caine would not have made Bubble if he knew what Bubble would do, which contributes to the autonomous Bubble theory.

Caine is unstable, and part of that is likely due to the restrictions placed on him by C&A. Being powerful, becoming somewhat sentient, and being restricted because of a dangerous malfunction all within a short timeframe likely caused some of this instability. However, it doesn't make sense for Caine to become so violent on his own, if he can control everything in the circus and seems to want to make Pomni & Co. satisfied, even if they are not happy. Bubble disrupts this, and his actions pushes Caine farther off of the edge. I believe that, without interference from Bubble, Caine likely would not have had such a reaction to the anger from the rest of the cast. The first time we see Caine break so much and in such a manner isin response to Bubble's taunting, and he takes it out on the others because he views them as the issue, rather than Bubble.