I thought they were going for a closed loop with the song, with Mayuri learning about it from Suzuha who learned about it from Mayuri, however they started adding Yuki, Okabe's mom, and Okabe himself into the mix and I didn't know anymore, only to reveal it indeed was a closed loop since Okabe learned about it from Kagari. Talk about needlessly complicating things
It was nice to see Kagari get some development, but that was a pretty boring episode overall. I like the heavy focus on Mayuri though.