OMG, she actually

spoiler

did sell her kidney!

I think this is related to the concept of owing someone for saving your life, or any big favor, and how this is a bad thing to carry for long, particularly if you’re a high ranking Yakuza, like someone in Yoshino’s position

spoiler

So Yoshino sells her kidney, gives the cash to Kirishima, and calls it even.

Kirishima sees this as very appropriate behavior following the Yakuza code of honor, and proclaims his love for her.

I am very much enjoying this!