Underangel: A Kid Icarus X Undertale crossover

When a little boy wakes up in the Undergrounds, he doesn't remember much. He remembers looking down a deep dark pit before falling down it but that's it.
He feels like there's something more to his life, but is not sure what. When he meets a young monster, he seems to be hiding something from him. Something from his past.
But what could he be hiding?
And why would he be hiding it from him?
What's this little boys name?
Well....
He's a fallen angel named ???.