directors pushed the love rival dynamic again because shonen fans, a primary demographic of DDD, are thirsty for male vs male dynamics...kind of tiring imo

However I think that title suits Aira the most: Aira is THE love rival of DanDaDan, since Momo is the MC, and she acts as one of those standard rivals mentioned before as well, just less edgy because she's a girl. She respects Momo, but also made several moves on Okarun and caused one of the first major developement for both.

If I had to compare Jiji to someone who is a "rival", it'd be Minori from Toradora, he's basically her, but male