What season and episode of Sailor Moon does darien Serena fid out rini is their daughter?

Darien and Serena don't find out Rini is their daughter until the third season, SuperS, episode 35, "The Little Lady and the Prince of Dreams".

It's a big reveal that takes a while to happen, and it's full of emotion and drama as both Serena and Darien come to terms with the truth.