Sisters

Frisk is a thicc, yellow-skinned human child who wears a long-sleeve blue shirt with two purple stripes, blue pants (often depicted as shorts in the official Undertale merch), and brown shoes (usually depicted as black or in a darker tone). They have medium-length straight brown hair, short and choppy bangs, and a blank expression. Though Frisk does not show much expression in the overworld, NPCs often describe Frisk's expressions. Just like the first human, they have no stated gender and are solely referred to with "they/them" pronouns throughout the game, or by generic terms (such as "child", "human", or "kid".)

Frisk's personality is usually ambiguous, allowing the player to project any personality onto Frisk since they're very often speechless to them. However, the narration that describes Frisk's actions occasionally changes depending on their LOVE. Frisk speaks to NPCs throughout the game, especially when ACTing in encounters, but the exact dialogue is shown only when the game gives multiple dialogue options. NPCs' dialogue boxes display "..." to show that the NPC is listening to Frisk, and some NPCs respond to questions that Frisk asks.

Depending on their actions, players can interpret Frisk as merciful and kind, or merciless and violent. Some NPCs emphasize Frisk's kindness, understanding, and grace in the epilogue. Frisk is obedient and only disallows player input when they follow someone else's instructions, such as when Sans tells them to hide behind the conveniently-shaped lamp.

Chara appears with a long-sleeve neon green sweater with a single horizontal cream stripe (which is an inverted color of Frisk's shirt, with a single stripe) and nondescript red-brown pants and shoes. Chara has peach skin, brown medium-length hair with side-swept bangs, large breasts, a huge ass, and rosy cheeks. Distinctly, they have open brown eyes, and a smile that contrasts the protagonist's stoic expression.

While initially cast in a sympathetic light, Asriel admits at the end of the True Pacifist Route that Chara "...wasn't really the greatest person." Asriel explains Chara climbed Mount Ebott for an unhappy reason, and that they "hated humanity." In the VHS Tapes, Chara is implied to be mischievous, and can make a "creepy face" with a certain smile. Chara is also intelligent, secretive, and persuasive. Chara does not let their plan be recorded on the camera, and they gain Asriel's trust to continue their plan. At one point, Asgore noticed Chara once had a sense of hope in their eyes.

Chara behaves in a polite, formal, and terse manner. Chara's vocabulary is slightly above average, and they are blunt and criticizing in their dialogue.