Ninjibot
Nikkō and Iruka met in their early youth. Since Nikkō was not a trained shinobi, she and Iruka did not meet during the Academy. They often saw each other in passing throughout the village. Iruka recognized Nikkō as Senju Shiori's daughter - the grandchild of a legendary shinobi. This led to many, Iruka included, being intimidated by her. It wasn't until Nikkō's 12th birthday - an subsequently Naruto's day of birth - that she and Iruka formally met. After getting in an argument with her grandfather, Nikkō fled home and was in the middle of heading to the Konoha Graveyard when the Kyuubi attacked. While trying to go to his parents, Iruka heard Nikkō's screams after a building collapsed on top of her. While many were worried about the attack on the village, Iruka single-handedly rescued Nikkō talking her through the process and keeping her focused on escape. After rescuing her, Nikkō and Iruka developed a close bond - eventually getting close enough to date.
By the start of the series, Nikkō and Iruka are not yet dating but are pretty close. Nikkō, unlike Iruka, harbors a fear of Naruto, and thus keeps her distance from Iruka when they're around each other. After Iruka is saved by Naruto by the attack by Mizuki, Nikkō's perception of him changed. Realizing that she could have lost her dear friend, Nikkō realizes that she has special feelings for him but is apprehensive about revealing them - afraid she might ruin their friendship.