Finally dropping by~
Ooo, in Ending 1, there are two tracks! The first one you hear at the start is called "The Edge of Reluctance" by Moximog, and the one near the end, right before the final lines, is "Unraveling Doom" by Bismii.
As for the hand, that’s actually Rosario’s hand, not Sev’s! And yes, the light and butterflies are packed with both symbolism/aesthetics. If you take a closer look, you’ll notice how it differs from the other hallucination CG— that might be a little clue for you!