Jujutsu Kaisen: I Just Came Back to Life, and Kenjaku Mistook Me for His Younger Brother?

[Native protagonist, sweet romance, dual domains, no System, Hidden Inventory, same generation as Gojo and Geto, exhilarating battles]

“Jingong Ren, it’s time to wake up.”

Jingong Ren: “Wait, Kenjaku, did changing brains make you stupid? Why are you so set on being my big sister?”

Kenjaku: “Forget that for now. When exactly are you planning to fight Sukuna?”

Jingong Ren: “Either could happen. That’s my answer.”

The early part is a little slow to warm up, focusing mainly on daily life and laying the groundwork for the relationships.