This is a strap, keyholder, or charm.
Kotori from "Sweetness and Lightning" gets a cute Bocchi-kun rubber mascot! She measures about 5.5cm by 6.5cm.
“Bocchi” comes from the Japanese phrase “hitori bocchi”, meaning ‘all alone’ or ‘all by oneself’, and this series tries to depict characters in a position representative of this phrase—looking a little lonely and in need of your attention. Be sure to give them a special place in your collection!