Princess Penny is the princess of Dokapon. She is a sweethearted girl and cares about her kingdom enough that she doesn't mind the marriage proposal reward her father suggests to adventurers who succeed at saving the kingdom from poverty. However, in Dokapon! Ikari no Tetsuken, Dokapon DX, and Dokapon the World, she doesn't appear at all, instead assistants will be here.
At the end of the game, the player with the most money will get to marry her. This happens regardless of the Character's gender.
In Oukoku IV and Journey
Princess Penny is much more rude and spoiled. She will often berate players who fail to meet her expectations in that game's story mode, but only in the dress part.
In 3-2-1 and Kingdom
If a Magician or a female character is the winner, the ending is slightly extended, showing that Penny appears to gladly accept the idea marrying a girl, despite her father's complaints about the pairing.