Gakuen Kaiketsu Kururi!

The protagonist is a school troublemaker who finds himself in a jam--his father has accumulated a large debt and has skipped town and it's up to you to repay the debt. The secret to the debt repayment is in getting 6 girls (teachers and students) you're involved with to help you raise the money.

[Edited from a post on Hongfire by davidlu9837]