Charisk? I love that ship. Consider it as an OTP for the main universe. I love how they're personalities blend in together. It gives a unique chemistry between for one being a pacifist and one being a neutral runner. They have both had each other (Except Sans cause he killed Frisk at one point) in every single timeline and probably helped them get through their fears and nightmares from that said path.  For instance, this could generate Hurt/Comfort, also fluffy fics from this due to helping each other from PTSD of killing their loved ones.

The main problem of this ship is how Chara is implied to be dead and now acts as a narrator to Frisk is like wha? People have called it out for incest for both them being siblings or selfcest in that matter. Pffft.

The game never mentioned them being siblings or they are the same person. It just states that Chara and Frisk both have the same Soul trait, determination (A/N: Not really a soul traits .) doesn't mean they are brothers or siblings. Examples are people who have the same Soul trait such as Perseverance or Integrity but aren't even siblings for that matter. Making this excuse rather biased and one-sided.

Chara is their own person. After all THEY were the first human to fall and an adopted sibling to the Dreemurr household. So much evidence supports their existence before they became a ghost. For instance, the drawings, Asriel, Toriel, and Asgore's dialogues, etc. It proves that they have once existed before Frisk freed or kill them.

IF chara is the same person as Frisk, then the Goat Family wouldn't have disbanded from certain events. Asriel would still be alive and Asgore wouldn't kill any fallen human.

Conclusion:
I can see this mostly working in the main universe because they seem to be like mutuals in the hopes redeeming themselves for the better. At least the other could understand why they did 'that' rather than dunk them for their mistakes. I know Sans can be another option for Frisk but I don't think he'll be that forgiving in their journey of redemption. Plus I literally have a fond of polar opposites becoming a pair.

Bonus
Reapertale Charisk
Reapercore
Undertale
Storyshift

ARE BEST Charisk

Result

100000000/10