Talk:Rance 6:Walkthrough/@comment-24.93.143.205-20170111015436/@comment-97.91.239.199-20170116021108

By defeating each set of hannies a multiple of 10(10, 20, 30...) you get access to the underground area of hanni plains. It contains 3 locked doors(one of each color), each of which have 2000g chests in them, as well as a key to the Hanni castle. HOWEVER, I would very much recommend not bothering with it until you get Rizna's S weapon mission because you have to go into the underground for that as well(behind the green locked door), and the underground only stays open until you leave the map when the time you open it. The castle has two red cloud fights in it that should probably be left until post game anyway(well, one of them is 5 super hannies which isn't post game worthy but regardless) so getting the key before then isn't necessary.

Note: You can get around needing to buy two sets of keys for the last clear by not clearing the black hanny room until after you leave and rebuy the key set. E.g. (10 green, 10 blue, 10 red, 9 black - leave, rebuy, come back, 10 black, underground opens).

Tip for fast clears: Kanami's aoe move does damage to hannies and if you upgrade it to not have a charge is very helpful for quickly killing the little bastards(at least the random encounters and the green hanny room), and she acts before all of the hannies so all the better.