Mystefied

The crescent blade absorbed the strong current of electricity before it could injure Lucien's fingertips.

Lucien finally knew that the picture contained a mechanism that would only be unlocked by the original owner or by the person this mechanism was intended for. Hence, he went to the other rooms to search for pictures. 

Because he noticed the creator would hide magic inside a picture. As if the image captured inside means a lot to him. The more pictures with hidden mechanisms he found, the more he noticed that one person was in the same pictures. 

From a little girl to an adolescent young lady. 

It was Isabella. 

The bride ghost, whom Isabella referred to as Lisa, was a child adopted by the Priest at the same time as Gabriel. The three are roughly the same age, and they grow up together. Gabriel was supervised by the Priest. He wanted to have Gabriel follow his example to the priesthood.