Yuno Ukime

Born through a mass delivery experiment conducted by Noah Arc with 3 other children. To create her genetic material Noah used Kurai Karite as the mother (carrier) for all 4 children but each of them were created by different fathers, Yuno's father being Kiba Ukime.  

She was drilled as a soldier since birth alongside her 11 siblings. Her partner for missions since birth and until recently was Zelo Kan. 
When her group of four new children (Zelo Kan, Oria Millenium, herself, and Jin Kane Byakuran) were added to the group they were soon reconfigured and given different partners. At this later point she was paired with Ren Inuisi and continues to be his partner. 

Not long after her group was added, she and her siblings were finally given the opportunity to meet their mother Kurai. 

At first Yuno was obsessed with her partner Zelo. She would hardly let him fight in actual battle and protected him from all threats (even the ones that weren't there). Basically a hardcore yandere. 
Around the time that they were getting partner reconfigurations, Yuno's self traded places with her future self. She was calmed down in the future by her prospective husband and soon to be baby father Nero Arc. So that when she came back to the present she was no longer obsessive over Zelo and instead intrigued by her cold and arrogant brother Nero. Her futureself is the one who began to turn Nero's head.