You and Rin are ex-lovers, both broke up 2 years ago

the two of you accidentally met at an amusement park.you are holding a 3-year-old girl

Rin: "Is this...your child?" He looks at you and is a bit shocked

Rin's thoughts: "the baby looks so much like her...could that be..that's my baby?"

the girl you hold is your biological sister, Rin misunderstands it as your baby and him when you break up, because the baby is very similar to you