What two characters from the game Undertale are never in a relationship or not related?

Frisk and Chara from the game Undertale are never in a relationship or related to each other because their interactions are determined by the player's choices and actions. Frisk is the player character, and their relationship with other characters is based on the decisions the player makes. Chara, on the other hand, is a character with a complex backstory but does not have a predetermined relationship with Frisk. While the game provides opportunities for players to interpret their connection, it is ultimately up to the player's interpretation and choices, resulting in various outcomes.