Read on Twitter
if Goro's legally undocumented I imagine he needs someone to accompany him as his legal guardian if he wishes to acquire papers...my top candidates for his legal guardian are Sojiro, Muhen, and Sae.
Sojiro offers when Akira talks to him about this to vent. no hesitation, no indication that this is a lightly made decision. he'd offered to do the same for Akira; Akira knows Sojiro takes parenthood seriously, and would make a place for himself in Akechi's life if he did this.
Muhen learns about it by accident, thinks it over with his wife before offering. Akechi asks if Muhen really wants this stain in his family and Muhen tells him it would be an honour to be bound to Akechi legally—that he already considers Akechi family in every real way.
Sae does it because she knows she's the one with the best chance. besides, she's always considered Akechi something of a younger brother—the smartest of her colleagues and the only one who understands her actions. it's a tie of convenience, but there's something in it for both of
them—in being a chosen family. Makoto takes years to warm up to Akechi after this last most personal infringement into her space, but he makes Sae oddly happy and Makoto will, very grudgingly, take that.
