How can I play a character like Chara from Undertale (with a really strong knife) in D&D?

In my friend’s D&D game, I am trying to find a way to play a character like Chara/Frisk, so the simplest way I thought I could do that is with an overpowered knife.

I was looking at Unearthed Arcana and I found the Psychic Warrior martial archetype for fighters (from UA: Fighter, Rogue, and Wizard), which was perfect, but then it got revised into the Psi Knight (in UA 2020: Psionic Options Revisited).

How can I create a character whose class allows them to make their melee weapons/attacks stronger, and who is able to do long-ranged energy slashes?

Of course, the former is more important than the latter.
I also don’t want paladin, rogue or ranger stuff. (The reason I don’t want rogue is because it’s more of a stealth class and I just want to kill people.)
I’m fine with Unearthed Arcana content; in fact, I would prefer it.