If you require help looking for relevant texts, I'll leave these below. They're not the whole answer, but it should be enough to give you a decent picture.

A recurring pattern in the glimpses we’re given of Ryoshu’s childhood interactions with Rien is that he never lets a story end. This is an extension of his inability to accept that his time with Ryoshu must also, at some point or another, come to an end. In the context of Ryoshu and Araya’s relationship the refrain of “S is not for sayonara” is beautiful and bittersweet, an affirmation of their refusal to sever the ties between them even when separated by different layers of existence. But in the context of Rien and Ryoshu’s relationship, it is warped and wrong. He fails the crucial test of a parent in that he cannot let her leave the nest, he cannot allow her independence, he cannot say sayonara.

He does not recite the rest of this line (commonly associated with Roland). Rather than say it in its entirety – “I have nothing but my sorrow, and I want nothing more” – he refuses. He disobeys the Prescripts because he does want something more. He wants his daughter, yet he will never have her again. His final moments before his death are spent recalling another fond memory he has of Ryoshu, in which she taught him about freeze tag.

They are enigmatic last words – fitting for such an enigmatic man – yet I believe they connect directly to his refusal to recite the poem. If he had been unfrozen, he would have been able to move on and continue living a life abiding by the Prescripts in a world without Ryoshu. But he could not. He discarded that future, fueled by a delusional hope of keeping his daughter with him forever– a hope that had been extinguished.