I'm going to interpret this for a second that Rin playing as her brother with Miku's voice and dance, harboring a twincest/brother complex love over Len. Len is disturbed by this.
I just want you to think from the heart
Kimi ni kokoro kara omotte hoshii no
The full line is:
I just want you to think from the heart that I'm cute
Kimi ni kokoro kara omotte hoshii no kawaiitte