Interest bearing securities with management share

Dear all,

Kindly advise suitable option for the following scenario. In case, a private limited company wants to give away 25% equity to investor for amount of investment made in Company with right of 12% interest on Monthly basis. Company do not want to refund amount invested as its not debt.

I feel there should be issue of equity shares as well as non-redeemable debentures. Please suggest suitable instrument to be issued and key points to be kept in mind.

Thanks to all for reading this..

Vipul