Notes:

Is this too much? If so, sorry. The information is from Axetale's official tumblr.

Chara was a twisted creature even before the Hunger took the Underground. It makes sense that they’ve only become worse since. The violence of the monsters in the Ruins (and subsequently their violent ends) gave Chara a power they hadn’t felt since their first run with Frisk, but it wasn’t quite enough.

They manifest in the form of a small, partially decayed, maggot-riddled child with gleaming, intelligent red eyes. Adorned around their neck, a memento of their time with Frisk. A tattered, dusty, spectral scarf.

When Aliza fell into the Underground, Chara saw in her great potential. But the girl would not be swayed by their honeyed and calculated words. For all the power Chara has gained in the years following the Hunger, they remain unable still to wander far from the flowerbed where their body was buried so many years ago.

So when Aliza threatened to slip beyond their grasp, Chara tore off their own smile, giving life to a heinous moth-like creature, their (literal) mouth piece to follow Aliza on her journey and try to coax her into actions that would give Chara a foothold in her soul.

They are very seductive, charismatic, silver-tongued and persuasive.