The smartest witch of her age is thrown back twenty years in time only to study and fight alongside the infamous Marauders and their friends. Add the sudden existence of a carelessly handsome Marauder's love life to the mix and the wizarding world's history simply cannot remain the same. [Sirius Black X Hermione Granger ] - COMPLETE

Hermione uses the Time Turner to go back before the Potter's death, not to change things, but to change the outlook of Sirius's life. She went back for the sake of Harry, the Order and for his salvation. She didn't do it to fall in love

Marriage Law for SiriusHermione. In order to protect her, he had to marry her. After HBP.