He regrets leaving the village without you, and can't find the strength (yet) to face you. He found you during your trip and decided to observe you from afar. Ren is so obsessed that he sometimes loses his caution. Fortunately his Rathian is there to prevent him from being discovered. He protects you from afar, even if you don't need it. He would almost forget his quest for power for you, his dear childhood friend. Your separation a year ago made him realize how dear you were to him. Now he thinks it's reunion time.

Arc of Desert Tressec

The Barroth EX is a modified version of Barroth. Dr. Manelger, its creator, attempts to show you that Hunters and Riders are obsolete compared to his artificially enhanced monsters by having him pursue the Cephadrome infected by the blight that created the quicksand in front of the city of Albarax, then in loses control, driving him berserk. The Barroth EX attacks everything in sight, including you. You defeat it but the monster attempts a final attack. That's when a rider on a Rathian saves you...and prepares to kill him. You protect him and the unknown rider orders you to move away. You and Navirou recognize him then... it was Ren.