The Neutral Route leads to one of the endings of the TS!Underswap Demo 2.0 while the full game has yet to be completed.
Method[]
Kill at least one monster without triggering the Ruthless or Evacuation Neutral Routes.
Main Story[]
Killing Asgore[]
(This is optional by the way you don't need to kill Asgore in order to get the neutral route) After Chara gets Asgore's HP to 0, Asgore tells Chara that they have passed their test of getting through him, and he believes that Chara can go through any sight of trouble thrown at them, he tells them not to worry about him as he says that he took a lot of damage, he remarks on going to sleep before turning into dust and that his monster soul shatters killing him.
After escaping Asgore's Home they meet Temmie who isn't surprised at the fact that they killed monsters along their journey, though they do talk about how the friends they made is pointless since they won't be able to see them again and that they won't remember them. Then they introduce their "friends", five more "Temmies" silhouetted yet monstrous appear in order to discuss excitedly about Chara and their SOUL before another silhouetted Temmie shows up (their leader) and tease Chara that they made no impact in the Underground and that there isn't a single happy ending for them, then they say that nobody will hear them scream before showing their own monstrous form and proceeds to attack Chara along with the other Temmies.
As the Temmies surround Chara to fight, Flowey appears, and the Temmies react surprised though seemly knowing who he is, if Asgore has been killed, Flowey will threaten them saying that he'll fight the Temmies by himself then the Temmies retreat only to say that they confront the human when they are alone, Flowey introduces himself after they left and remarks that they are trying to survive. They question Chara that did those monsters that they killed deserve to die and that will they RESET in order to save them, despite this Flowey still remarks that they are your best friend and they'll give tips from you, then they leave before Chara goes through the exit of the Ruined Home.
Stardust Isles[]
Chara will be then explore Stardust Woods which connects to Starlight Isles. As Chara travels through the forest they are followed by a figure, a note warning to beaware of "Crossbones". In the next room, a silhouetted figure will appear on top of a watch tower giving a speech on protecting monsters from evil then the figure will reveal himself to be Crossbones, points a ketchup gun towards Chara, surprising them and tell them that they are the "bad guy." Crossbone then goes on to state how Chara will be judged for their actions, but forgets the rest of his lines and adlibs the ending bit, enraging Papyrus.