You cannot specify criteria like "replies to a certain account" with filter stream. However, it is possible to detect if a tweet is a reply to a certain account by using Status#getUserMentionEntites(). The code will be like this:
public void onStatus(Status status){
for(UserMentionEntity mention : status.getUserMentionEntities()){
if(mention.getScreenName().equals("yusuke")){
// do whatever you want
break;
}
}
}