Saji and Issei have a friendly rivalry going on because they are both Pawns, they both harbor feelings for their masters, and they both have Dragons in their Sacred Gears. At first they did not care for one another (due to Issei being one of the Perverted Trio and Saji's cocky attitude), but when the "Excalibur Destroying Squad" was formed, the two shared their biggest dreams and eventually found out that they are alike one another, in that they share each others desire to marry their masters. Their relationship to each other is strong enough that Issei even went as far as describing them both as "War Buddies". Their friendship developed further as the series progressed, as Saji expressed sadness and grief when Issei died, even promising to avenge him.
Despite being good friends with one another, Saji is very envious and jealous of Issei, even to the point of seemingly developing an inferiority complex towards him. While Issei has made tremendous growth in strength and has made his master his girlfriend, Saji has felt left behind in comparison. He laments the fact that he will never surpass Issei in power, no matter how hard he tries. It is not until he states his dream and finally obtains his Balance Breaker that he stops comparing himself to Issei.
Saji is a Pawn in Sona's Peerage. Sona is also the woman that Saji is in love with. He has even stated a desire that if he could ever sleep with her, he would try to get her pregnant so that they would be forced to marry. Sona, while having some affection for him, has demonstrated no romantic interest in him, preferring men who are at least her equal in intelligence. She states that she sees him more as a little brother, and that she does not want to touch him when she knows that two other members of her peerage have shown romantic interest in him.
Momo has a crush on Saji whom she affectionately calls "Gen-chan".
She has a crush on Saji and has a love rivalry with her senior Momo Hanakai, who is also in love with Saji.
Vritra is one of the Five Great Dragon Kings known as the Prison Dragon who resides inside of Saji's Sacred Gear(s). Their relationship is similar to that of Issei and Ddraig's, they get along just as well as Vritra considers Saji as his "other half".