Leave Kimahri, Yenke. Kimahri is small Ronso. Kimahri so small can't see Yenke and Biran's faces.
Biran is a powerful Ronso warrior who respects those with strength to match his own. His victory over Kimahri in a battle left tension between the two, and Biran has behaved antagonistically toward Kimahri thereafter, deriding him for being hornless after breaking Kimahri's horn. Biran is a proud Ronso and is willing to show respect to those whom have earned it in some way, thus leading him to praise the summoner Yuna and eventually even Kimahri.
In the time before the events of Final Fantasy X, Biran is known as a hero, most likely for being a great warrior. Biran fought a fierce battle with Kimahri Ronso, and after Kimahri lost, he refused to admit Biran had beaten him, and so Biran broke his horn bringing great shame on Kimahri.
Ten years later Biran and his companion, Yenke Ronso, meet Kimahri in Luca where they taunt and fight him, but with no resolve, because Kimahri is interrupted when he learns of Yuna's kidnapping. When fiends attack the blitzball finals, Yenke and Biran are among the heroes fighting them off-screen. Later on, the duo meet Kimahri and company along the Moonflow after bullying Wantz and warn Kimahri about summoners disappearing.
Finally, Kimahri meets and fights Biran and Yenke one last time on Mt. Gagazet. He regains his honor as a Ronso by defeating the duo in a two-on-one fight and afterwards, Biran, Yenke, Maester Kelk Ronso, and all the other Ronso promise to fight off anyone pursuing Yuna and her guardians on the mountain. When Seymour Guado follows them he is attacked by the Ronso, but Seymour goes on to slaughter any Ronso in his path.
A couple of years later, if Yuna says something favorable to a Ronso, he remarks "Biran and Yenke rejoice in Farplane". This proves that even though some of the Ronso are gone, they are not forgotten.
Biran is fought on Mt. Gagazet alongside Yenke. Kimahri fights them alone.