Frisk is really the fandoms perceptive of Chara, as well as Chara is the fandoms Frisk.
Frisk=WARNING : This name will make your life hell.
Chara="The true name"
So really, nothing special happens when you name the fallen human Chara: it just tells you “the true name.” Naming the fallen human Frisk will activate hard mode. It doesn't matter which route you take—genocide, pacifist, or neutral. Additionally, hard mode only lasts until the end of the Ruins.
