Character Design
The artist who does the character design for Disgaea,along with the cover art and other illustrations are done by Takehito Harada.Some could say that with the help of Disgaea,Harada has attracted more fans with the type of design Harada uses to design the characters of Disgaea.You can visit Harada's site here:

Harada's site

Harada has also done artwork for Phantom Brave,Makai Kingdom,and Disgaea 2. His mascot,Pleinair has been seen in Disgaea 1 and 2,and also in Phantom Brave.
Her first role in Disgaea 1 was being the guide that allowed you to see the Dark Assembly,it seems she only talked to Laharl and no one else.
In Phantom Brave,she was only seen in the background in one of the cities.
And last,her recent appearance was in Disgaea 2,she takes the role of a news reporter,but without a voice.Her bunny friend,Usagi does all the talking for her.There really isn't much about this character,what her personality is like,or what likes/dislikes.It's possible to guess how she can be through the illustrations done by the artist,and more than likely only the artist knows how Pleinair really is.Harada fans also admire this mascot,to the point they wish you could have her join your team in the game,unfortunately,that will probably never happen.

Edit:
Okay so it seems you can recruit Pleinaire,but only in Disgaea DS and Disgaea 3! <- back