In Disgaea: Hour of Darkness Flonne is a simple angel trainee who is dispatched by Seraph Lamington to kill King Krichevskoy. On arrival in the Overlords Castle Flonne is spotted by Laharl (Because she woke him up with loud talking to herself) due to this she runs off. After finally catching up to her, she joins the party in an attempt to discover if demons can feel love or not. During the rest of the game, she tries to make Laharl understand love. (Which reminds him of his dead mother) As the game progresses Flonne ends up helping Laharl become overlord,which makes her a traitor to Celestia. At the end of the game, she is killed as punishment and becomes a Fallen Angel (However on the normal ending Laharl dies reviving her)
In Disgaea 2: Cursed Memories Flonne has no actual part in the storyline, she becomes a playable character after the player completes the optional mission "I want to fight an Overlord!" Upon completion Flonne decides to stay with Etna in Veldime, she also tries to get Etna and Laharl to stop their fight against each other.
In Disgaea 3: Absence of Justice Flonne has a minor storyline plot, she appears post game with Etna and Laharl to fight Mao,who they believe to be the legendary overlord who has stolen their things. After defeating them, Flonne (along with Laharl & Etna) joins your group. She also appears on an alternate ending pretending to be Maos mother.
In Prinny : Can I really be the hero? Flonne is an downloadable content boss, she fights on a pogo stick however.
In Phantom Brave Flonne battles Ash and Marona with Etna, she also appears later with Laharl and Etna.In Makai Kingdom Flonne challenges Zetta, claiming to be a warrior of love.