etna, prinny, flonne, laharl, mid-boss, and 6 more (disgaea and 1 more) drawn by yamamoto_keiji

Well, it's been forEVER since you asked, but I'll answer anyway.
This is from the official Disgaea light novels, the fourth volume specifically, "On Love (Part One)".
Sakura's a former angel who's obsessed with collecting every single sword ever. Her eye on Gwen’s Excalibur, she kidnaps Gwen to the Netherworld and makes her work there for 200 years. There's some weird timey-whimey thing goin' on, where two timelines converge...it's pretty confusing. (Oh, Disgaea.) I guess it makes sense if you read it? In the 5th novel, Laharl beats Sakura, and she hilariously falls madly in love with him and his strength. After that, she wanders the Castle halls, searching for Laharl lol.
There's lotsa info/summaries on the novels here, if you wanna find out more~ There're virtually no translations :(
(http)://community.livejournal.com/cyberdance/190266.html#comments