Yep, that was it... she did the ultimate move.
It's a sentimental bucket-list achievement, in the form of a physio-emotionally climactic show of intimacy to the one she had truly loved, in near-perfect collaboration with her dear slightly-rowdier self from a decade ago. With this, Operation [Selfcest-to-Saki Threesome] is officially a success, a high-value scene to commemorate her departure from that time period.
Apologies, I get ramble-y af when sappy sht like this happens. (*saved) Final Chapter Let's Go