While Nathan is in the elevator, he is also trying to recall the past.
It is true that Ryzel had a younger sister. Their small group back in college knows about it. That's because Ryzel is always missing on his sister's death anniversary. He probably wanted to be alone and avoid showing them his weakness.
But Nathan remembered that there was a time when Louisa stayed on Ryzel's side on his sister's death anniversary. He has no idea what happened. But when Ryzel returned the next day, he was in a good mood and the was not a trace of a gloomy atmosphere around him.
Nathan knows that his little sister died at the young age of eight because of lung cancer. Ryzel was three years older than his sister. At that time, he was the one who took care of her because their parents were always on a business trips.
