Nana first made an appearance together with Momo in Chapter 97 of the To LOVE-Ru manga. They were responsible for the Trouble Quest, an RPG game that they programmed to see the true character of Lala's friends. After seeing that Lala had great friends surrounding her, they returned to Deviluke. A few chapters later, they went back to Earth after escaping from Deviluke and their studies. However, they forgot that Zastin was also staying on Earth, and was instructed by Gid to bring the twins back home. They tried escaping, but when Nana and Momo started fighting each other, Zastin, Maul and Smutts were able to catch up to them, and a battle ensued. It was revealed that Nana and Momo also have D-Dials, but instead of gadgets, they were able to summon animals and plants, respectively. In the end, they defeated Zastin and his henchmen, and they convinced their father that they're going to stay on Earth with Lala.
During Nana and Momo's stay in the Yuuki household, they created their own house in the attic using space distortion. They also took care of all their necessities to avoid bothering Mikan for cooking, cleaning, etc. However, they still come down sometimes to eat Mikan's cooking.
Throughout the series, Nana unconsciously develops affectionate feelings for Rito. Of course, she consciously dislikes him and thinks of him as a beast! Because of this, Nana usually has dreams of Rito "sexually" advancing towards her and she screams out "You beast!" in her sleep. Whenever she's asked of the situation, she glares and says, "Oh that Rito.....he's a beast!" and says no more. At this point in time, Nana was completely confused whenever her sister said, "Oh, I can always be Rito's mistress".
In To LOVE-Ru Darkness, Nana, along with her sister, become Sainan High's students, she makes friends with a girl named Mea and she gets shocked whenever Mea admits something perverted to Rito. Eventually, the friendship between Mea and Nana becomes very strong; however, Mea turns into her semi-weapon form and tells Nana that their friendship was not real! Nana was petrified and traumatized after she saw Mea's true form and personality.
Rito tried to console Nana. When that didn't technically work, Rito embraced Nana. With that hug alone, plus some encouraging words about friendship, Nana finally realized what she had to do. She had to approach Mea and "opened her heart". Obviously, Mea used her semi-weapon abilities to scare off Nana again; however, Nana has shown a huge amount of courage and she faced the heartless semi-weapon. Nana stood there boldly and she confessed her care for Mea. This somehow opened Mea up. Finally, Mea understood what a friend truly was. This part of the story has shown Nana's bold bravery against something quite deadly, and this has shown Nana starting to open up to Rito. In fact, she even tried to sleep in Rito's bed afterwards (although inadvertently halted by the presence of Momo).