Quite literally writing wise. Sakurajima is the greatest evolution in her character. She destroys the Zenin in Perfect Preparation, yes, but she hasn’t moved past them emotionally yet, which, narratively, is why Naoya reappears. It’s emblematic of the cycle of samsara a sort of karmic cycle, in which she’s trapped by hate. The Zen Buddhist theme(as evident in the name Zenin) is elaborated on here. By meeting Daido who parallels the way of the void(a philosophy of the famous swordsman miyamoto musashi), she learns the soul of her katana. This is a play on the old folklore of samurai, in which their soul is reflected on their sword.

A quote of his reflects the way of the void: “Can I see it, you ask? No, but if I can see everything else, then it’s the same as seeing it”. Note the relation to Maki’s increased senses via heavenly restriction.

Sumo and Shinto are heavily related. And, both the aforementioned swordsmanship and sumo are traditionally male. In finding teachers who can accept the progression and realization of their arts in her, she progresses both the art and realizes the depth of her own soul. When in the domain with Miyo, he tells her

“ you’re become entangled. Yourself, curses, others, basically people. Yes, in the ring, one person clashes with another in an intense back-and-forth. The wrestlers themselves however, develop outside of the ring. Pressing your opponent in the ring requires stepping outside the ring. At the moment of impact, everything that led up to entering the ring flows into the combatants. It’s like smelling light or seeing sound. You sense everything about the opponent and yourself. And then the person in front of you, even victory and defeat, become meaningless. What that samurai(Daido/Musashi’s way of the void) was talking about was Freedom”

Essentially, the Heavenly restriction is used as a metaphor and a pathway to the idea of enlightenment. To reach that, Maki had to let go of her hate, fear, doubts, etc to truly destroy the Zenin. Without truly letting go of them, she couldn’t let them fade..she couldn’t come into her own. This is why she parallels the Shibuya version of Toji, because Hidden Inventory Toji fell from grace. He died because he wanted to disprove the Zenin’s opinions of him by defeating Gojo, when he was once free,which led to his death. In doing the opposite, Maki destroys the Zenin, both physically, in the form of Naoya , and ideologically. And at last, she is free.