So imma explain a few things :

The games plot is that you the player are one member of a squad "Delta 7"(Might change the name later) of the human side of the war between humans and monsters

From there you can choose a path : Similar to undertale there are 3 endings (A secret 4th one) in total.

Ending 1 - Victory :

You fulfill your given duty and hold back the monsters resulting in human mages being able to create the barrier.

Ending 2 - SOLO :

A feature in the game is that delta 7 is the "Seven human souls" thats mentioned in the original undertale (Justice,patience blah blah blah) and during battle they can "Fall" temporarily being unable to assist you in battle.

When this happens you get a prompt to "HEAL" where you order kindness to heal said FALLed teammate. You can see where im going here.

Or,you can just...not...heal your teammates.Resulting them to die at the end of the battle do this for all your teammates and you get the SOLO ending after beating asgore.

Ending 3 - Neutral :

Similar to undertales neutral - except this time it's your teammates have some,leave some.

Ending 4 - SURVIVOR :

I will reveal this later.