View Solution

The mansion is one of the two locations where you can get the disguise for Aiko in Nagoya (the other location has two naked male civillians getting massaged). There's a rock in the courtyard that you can use for "Good Old Rock...Nothing Beats That". There's also a flower pot on a balcony outside for "Sunflower Samura".

If you have killed the enemies at the mansion, the achievement will pop up once you complete the level.