The most important relation for Ichijou is the one with Kaname.
Since Kaname is a noble Clan and a pureblooded vampire, for all he represents a prince, a sort of god, someone with whom no one can stay together. So all call him "Kaname-sama" and make the possible to enter his favours, but anybody is interested in him for a sincere friendship.
Ichijou is totally different from the others. He calls Kaname simply "Kaname" and talks with him as a true friend. Kaname knows that Ichijou is the one that could sacrifice his life in order to save him, but his feelings are pure, not dictated for a personal interest or for Ichijou's grand-father's plans.
Kaname and Ichijou are best friends, they stay together for the major part of the day (and night too... this meaning is ambiguous XD) and they're respective very sincere. Ichijou says to him what he wants, even if Kaname could be angry.
Their relationship is very sweet and based on respect and loyalty. Kaname doesn't consider him a friend as Idou and the others, but he's more like a brother. When Asato says to Ichijou to control and betray Kaname, he declines because he will always remain by his side (I love this part of the manga!!), proving that he's a friend of Kaname and not his guardian.
Unluckily, in the last part of the recent chapters, Sara manipulated Ichijou in order to use him as her toy and put him against Kaname... I hope that she will die very soon! -_- And that Ichijou won't be controlled from a horror doll like Sara. =_=
Credits for the scans to VK Scanlations