Mahito first developed this technique while he was close to death during the climax of his battle with Yuji and Nanami. Using death as an inspiration, Mahito was able to increase his power and unlock the ability to utilize a Domain Expansion.
Mahito's Domain Expansion is conjured by hand seals formed by tiny hands inside Mahito's mouth. This creates a large black environment that presents Mahito's target with giant hands clasped together to form a flower-like shape. Connected to these hands are multiple arms that grabbing one another to form a net pattern that surrounds Mahito's target.
Like all Domain Expansions, Self-Embodiment of Perfection increases the effectiveness of Mahito's Idle Transfiguration cursed technique by guaranteeing it hits the soul of the target every time. Nanami described the experience of being inside Mahito's Domain as akin to literally being in the palm of Mahito's hand.
However, a major drawback of this ability is that Mahito is forced to touch the Soul of anyone inside. This backfired when Yuji entered the Domain from the outside, causing Mahito to, albeit unintentionally, touch Sukuna's soul a second time, prompting the King of Curses to lash out at Mahito.
Mahito activated his very own Domain Expansion first time against Kento Nanami and Yuji Itadori. It immediately locked Yuji out and trapped Nanami alone inside the dimension. However before Mahito could use his cursed technique, Yuji broke into the Domain Expansion from the outside. This forced Mahito to touch Yuji's soul, angering Sukuna who slashes his body with two devastatingly deep cuts and severely damaging Mahito as his Domain Expansion collapses and he falls onto his knees defeated.
Later, he activated the Domain against Kokichi Muta. However, Kokichi used Ultimate Mechamaru Mode: Absolute Technique Charge Simple Domain to negate its effects and pretended to be affected to strike him back.
After his battle against Satoru Gojo which gave inspiration to him and his awakening of Black Flash, Mahito utilized his Domain Expansion for 0.2 seconds against Yuji and Todo. With this, he is able to use Idle Transfiguration on other targets without Sukuna being able to react.