The title of "Pontifical and Imperial" is a unique style within the Pontifical Imperial State of Rome-Ruthenia and the United Roman-Ruthenian Church exclusively used by the immediate members of the Pontifical and Imperial Household of the Pope of Rome-Ruthenia. That is, it is proper to the Grand Dukes/Duchesses of Rome-Ruthenia.
Further information
Pontifical and Imperial Household of Rome-Ruthenia · Apostolic Princess