Collect keys as usual and the floor will soon turn dark, once this happens the layout will change a bit and other keys will spawn, so, don't forget to check path already trodden (user "bob" stated there are ten keys to collect in total).
Ushris… Aside from what I think is a "one time thing" with the Holy Headpat skill, there's no real way to beat her, try to fend her off while depleting her energy and she'll escape from battle on her own.