Villefort said: Miku obviously stole Rin's cheezy love song dedicated to Luka, which would also explain Luka's expression.
Villefort said: Len was about to reveal it. Smelling something was up, Miku took the opportunity to take Rin's music while Rin was busy shoving Len in his noodles.
You have it all wrong. Miku stole Rins love letter to Len. Luka was shocked that she didnt notice Rins emotions for Len. And Rin shoved Len into his noodles so that he wouldnt hear anything.