>>528479960
I don't know exactly what Ralsei is, but I feel like I know what he represents.

Ralsei is a representation of everything Kris wanted to be. A boss monster just like everyone in his family, but still unique enough to be his own person. The comparisons to Asriel bother him because they wanted to be their person, not just Asriel's brother.
Ralsei is an idea that Kris came up with to cope with the pain of being so different from everyone they knew. Kris tells Ralsei to be himself and comforts him because Ralsei is an extension of himself, they want Ralsei to be himself because Kris wants to be themselves too. Kris wanted to be kind, caring, and compassionate but trauma of whatever it is they want through on top of the frustration of being different prevented that.
"Here is my cool character, his name is Ralsei. He's beautiful and kind and loves his friends."

>>528480469
Ralsei is thinking of (You), anon, he cares about you.
Take care of yourself, you can't be replaced; you are like no other. You are unique and beautiful just like Ralsei is, if you disappeared, something would be missing in this world.
You got this, anon.