It would be pretty difficult for me to only mention one duo, therefore I'd like to say some(。ノω\。)
Sakuragi & Rukawa
Hikaru & Akira
They're not only life long rivals, they are also life long friends. It's truly wonderful to share the same interest with others, they fight and have conflicts with each other, however, they improve their skills and receive motivations for each other as well.People can really feel their passions and dedications.
Mihashi & Abe
Tobio & Hinata
Touya & Yukito
Heero & Duo
Tieria & Veda (X
Tieria & Lockon (O