Aragami

A 'Yurei' medal is earned by completing the chapter without raising a single alarm.

The awareness level of guards is indicated on-screen with a meter that fills from white to yellow to red. If this fills fully yellow, you'll trigger the 'caution' state of a guard, while if it fills fully red, they'll attempt to blow their horn and raise an alarm. It's only this red fully-aware status that leads to an alarm being triggered, and if you can kill the guard before they blow their horn you'll still avoid the alarm.

To earn the Just the wind trophy, you'll need to complete any one chapter without raising any alarms; for the Ghost trophy, you'll need to do so for all chapters. You can combine this with either a 'no kills' or 'all kills' playthough, depending on which you find easier.