Natsume is at home early one evening when he hears a knock on the door.  He sees Tohko outside, asking to be let in.  But when he opens the door, there's nobody there, and a gust of wind rushes past.  Another Youkai is after the book of friends!
Only if you know their face and name.
Eso es en el caso de que 
conozcas su rostro y nombre.
Eso es sólo si conozco su aspecto y su nombre.
Mas preciso conhecer o rosto também.