Is Sukuna a conjoined twin?

Yes, Sukuna was originally a conjoined twin in his human form, which is one of the unique aspects of his character in Jujutsu Kaisen.

In the manga, it is revealed that Sukuna had two faces and four arms, which are an indication of his being a conjoined twin in his human life. The two faces represent two distinct personalities or beings that coexisted within him before he became a curse. However, Sukuna’s human body was far from ordinary; after he died and became a curse, he retained his multiple faces and limbs, which became symbolic of his overwhelming power.

This duality is reflected in his curse form, where he has two faces (one on the front and one on the back of his head), further emphasizing the idea of him being a conjoined twin or having a dual nature. His power as a curse grew significantly over time, and while the exact nature of his twin's role is unclear, it is believed that Sukuna's transformation allowed him to maintain his "dual nature" even as a cursed spirit.

This backstory helps to explain Sukuna’s two-faced appearance and his monstrous, otherworldly power.

For more information, you can check out the details on Sukuna's Wiki Page. or https://www.britannica.com/sports/jujitsu