A mask you put on to hide how dead you are inside.
1: Are you ok?
2: No I'm fine, (*A single tear runs down their face while smiling* ) I'm smiling.
Underfell but, every time Frisk dies, a flower grows on some part of their body and if they try to take it off, they die. Frisk is 18+ in this AU though. When Frisk meets Sans, Sans kills Frisk many times, but after several loads, Sans stops and join Frisk on their journey and then at the end of an emotional journey and many loads later, the flowers consume Frisk and Frisk tells Sans to use their soul to break the barrier and then Frisk dies, OH ITS SO SAD 😭
Person 1: FLOWERFELL IS SO SAD
Person 2: IKR