>>527987468
The message of Undertale is "Try not to kill, and try not to be killed."
I think its too early to say what Deltarune is about but it seems to be primarily about willpower and defiance against fate. To that end, I would say that FRIEND is likely a thing that seeks absolute freedom and views the entire world as its playground. A toxic Friend in name only that seeks to control you, that stands as a contrast against your true friends that support you.
However, I am no theory crafter, only a humble ass lover, so I will probably be wrong.