Yuta Okkotsu stands as one of Jujutsu Kaisen's more unique characters from its expansive roster. Starting as timid, lonely, and lost, he opened up and gained control of power after Gojo Satoru brought him to Jujutsu High. He learned how to effectively control and use the Cursed Spirit attached to him.
Years later, in the present timeline, he stands among the most powerful sorcerers to exist. Believed to be second in power to Gojo, he possesses an arsenal of techniques and tools that make him a formidable force.
Ever since his introduction and later the reveal of his Cursed Technique, many have wondered whether or not Rika is a part of it.
Disclaimer: This article is speculative in nature.
Jujutsu Kaisen: Rika's role in Yuta Okkotsu's Cursed Technique
Before delving into Yuta's Cursed Technique, it would be beneficial to understand what Rika is. From Jujutsu Kaisen 0, the Cursed Spirit Rika originated from a Curse placed by Yuta on Rika Orimoto as she was dying. Consequently, her soul attached itself to the boy and would manifest as a vengeful spirit.
However, following the movie's events, the Curse was broken. Orimoto bequeathed the remnants of her will to the Cursed Spirit, symbolizing a manifestation of her love that she left behind to protect Yuta.
So in essence, the present Rika is a husk of the original, identical in every way but far less volatile and more obedient. She is completely cooperative with Yuta at all times and acts solely with the intention of protecting him.
Rika is not Yuta's Cursed Technique
Not exactly Yuta Okkotsu's Cursed Technique itself, Rika is an aspect of it. As seen in the manga, the boy's Innate Technique is "Copy". Using it, he can copy and utilize other Innate Techniques when required. This is where Rika enters the picture. Barring ingesting, the conditions for "Copy" are yet unclear.
However, by ingesting a part of the target, their technique can be copied. For instance, Rika devoured Takako Uro's arm which allowed Yuta to use Sky Manipulation. Again, in Jujutsu Kaisen chapter 251, Yuta was able to use Cleave (Sukuna's technique) due to Rika ingesting his 20th finger.
Essentially, Rika plays a role in Yuta's technique activation and usage. He is able to use "Copy" when attached to her likely due to the nature of their bond. Rika Orimoto's soul bound itself to Yuta when his Cursed Technique was manifesting thus ingraining it in her as well.
Additionally, she acts as a storage unit for the numerous Cursed Tools he has acquired. With immense physical strength and durability, she and Yuta possess immeasurable Cursed Energy.
In conclusion
To reiterate, the Cursed Spirit Rika is not Yuta Okkotsu's Cursed Technique, but more likely an aspect of it. Her birth coincided with the manifestation of the boy's Cursed Technique thus entrenching the two.
Apart from this explanation, there is another reason which can reinforce why Rika is not his Cursed Technique. In the three-way Domain clash in Jujutsu Kaisen chapter 179, even after his Cursed Technique burnout, Rika is still present there, which shouldn't have been the case if she was the Cursed Technique itself.
Later in the same chapter, it is stated that Yuta's technique hadn't recovered yet. This happens with Rika floating right beside him. If she was part of the technique, then she should have disappeared when it burned out.