Reincarnated cuz he wanted to. He don't underestimate anyone and uses his magic, but the world he reincarnated into considers magic and swordsmanship bad.
THE MC ATTRACTS THE CROWN PRINCE FROM ANOTHER KINGDOM. HE FELL IN LOVE WITH HER AFTER ATTENDING THE SAME SCHOOL AS HER.
SHE LIVES LIFE AS A NUN WHILE A KNIGHT TRIES TO WOO HER (CAN'T REALLY SHOW HIS LOVE TO HER)
MARRIED TO A DUKE WHO TRIED TO KILL HER WHEN THEY FIRST MET. DUE TO MAGIC, THE DUKE FALLS FOR HER AND WOOS HER. THEY BOTH MARRY AND THE MAGIC STARTS TO WEAKEN (?). THE DUKE HAS TWO PERSONALITIES WHICH ONE IS LOVEABLE AND THE OTHER IS HIS NORMAL SELF BEFORE THE MAGIC WAS CASTED ON HIM. THEIR ROMANCE IS BLOOMING. MC GETS REAL JEALOUS.
MC IS REBORN INTO ANOTHER'S BODY IN THE SAME WORLD. THE TIME IS THE SAME. THE MAIN GUY IS THE GUY WITH WHITE HAIR. THE GUY WITH BLACK/BROWN HAIR IS TRASH.
SHE DIDN'T WANT A BAD ENDING SO SHE DECIDED TO GET THE LAST BOSS (THE BROTHER OF THE CROWN PRINCE WHO'S FATE IS TO BECOME A DRAGON). SHE PROPOSES TO HIM. HER CHARACTER IS SMART AND STRONG.
Shikkaku Mon no Saikyou Kenja