If you want Asriel to trust you, you would have to mess with the code.
And if you want to mess with the code, you'll need an annoying dog.
If you want an annoying dog, you'll need a Pacifist ending.
For a speedy pacifist ending, you need Debug mode.
Or a Frisk.
Whichever comes first, I guess.
Chara: How many times to I have to say this, we made up! Besides I would never do the p-pacifist route. Ew. Annoying dog is annoying for a reason. I hate it. Relay on Frisk for something? Haha! That's funny!
Frisk: Hey! i can be very helpful!
Chara: I wouldn't take the Frisk.
Sans: OOOOHOHHHHOHHOHHAHAHAH! F-risk I get it!
Frisk: -_-'