Mello & Near
Mello and Near from Death Note have a very important and intriguing relationship AND Rivalry. This section discusses more of them alone and together.
Name: Near (Nia)
Status: Leader of SPK
Goal: Catch Kira/ Bring Justice
Other: Likes Toys
Name: Mello (Mero)
Status: Leader of his own Gp.
Goal: Catch Kira/ Have Power
Other: Likes Chocolate.
The relationship between Mello and Near is a very special one and I admire it a lot. First of all, both Mello and Near were orphans at Wammy's House. That particular orphanage guaged the children there to become possible successors for L. Near was always the "better" one supposedly, the better grades etc. while Mello was close behind. However, when L died, unannouncing his successor, it was suggested that they both take over. Mello, angry about this, left the house as Near stayed for another couple years where he appeared again to challenge Kira by heading the SPK. Hence, from the beginning we see their close relationship as well as rivalry to one another.
Soon afterwards, Mello and Near were pitted against each other with the Death Note (obtaining it etc.). It was in this moment that I really loved their relationship. Mello and Near share such a close bond that they can easily tell each others' actions. Even when Near did not know about Mello kidnapping in order to obtain the Death Note, he showed obvious signs of knowing. He knew that he loved chocolate and even later on, could tell what he could do, as Mello could tell about Near. Although they don't show it, I think that Ooba created Mello and Near to be twin L's basically. But, they cannot stand alone and need each other to survive and have a purpose.
As for the rivalry, I think that is pretty obvious. They are both trying to catch Kira and also succeed in doing what L failed in doing. They are racing towards the same goal, and what could be better than that?