Undertale, but it's Frisk VS Chara

So I want to make an Au were Frisk and Chara swap Era's but I want to give more variety and interesting things instead of doing an underswap Take, any ideas?

Jesus Christ, Chara! Even Frisk doesn't want to be around you right now! (Art by Sjui00) : r/Undertale

Chara and Frisk - Fandom vs. Canon by TobiMilobi on DeviantArt

Undertale Frisk & Chara Acrylic Stand Figures

Frisk vs Chara : r/Undertale

Frisk and Chara - Undertale by DeadlyFangedArtist on DeviantArt

I never understood the difference between Chara and Frisk, can someone explain, please? : r/Undertale

Who wins here, Season 1 GT Chara or Season 2 GT Frisk : r/glitchtaleofficial

Frisk Y Sans Vs Chara by santi2001 on DeviantArt

Undertale Chara lore, gender, age, and relationships