Enjin might not be Rudo's favorite person right now, but he needs to rely on whoever he can to survive on the Ground! Where you shouldn't misgender doctors voiced by Ryusei Nakao or expect to get a free pass to anything, especially when you're a Sphereite. But Rudo can show his thanks and gratefulness when he needs to.
The Ground! Where people have actually managed to build their own community and cities, where the women are just as beautiful, and where the emotional existence known as "Anima" cultivate and create Trash Beasts who can only be defeated by vital instrument users known as Givers! Hence Enjin's group: The Cleaners.
Does Enjin know how to get Rudo back to the Sphere? Of course not! But the Cleaners' boss might, so it's probably in Rudo's best interest to join up with them one way or another. Besides, Enjin already gave Rudo his first paycheck, because he's just that considerate a guy! Granted, it's pay he made from the clothes off Rudo's back, but you can't say Enjin at least didn't give it back to Rudo.
Cats in the Ground are just as mischeivous as they are anywhere else, stealing Rudo's money, but you shouldn't steal from people in general...otherwise you'll get on the bad side of people like Zanka (Yoshitsugu Matsuoka!) who doesn't appreciate ANYONE handling his Lovely Assistaff but him.
Thank goodness Regto taught Rudo the power of empathy! It actually CAN diffuse a tense situation without a fight! And Zanka makes a complete 180 and becomes Rudo's buddy instantly after a proper apology! It looks like they'll have a nice, beneficial, mentor/protege relationship! All Rudo has to do is seal the deal with a nice, bright, smile!
Welp, never mind, Rudo can't smile to save his life and Zanka doesn't like to be disrespected in any form. Next thing you know Zanka's insulting Rudo's mission to avege Regto and we get a Giver vs Giver fight.
Rudo may have the ability to turn anything into a vital instrument, but Zanka's mediocrity means he's better trained and skilled, and that gives Rudo a heavy disadvantage...but it's to Rudo's own advantage that he grabbed a plunger with poop on it, because Zanka REALLY can't handle that. Next thing you know they're engaging in a chase sequence, including a Scooby-Doo door moment, and Rudo is winning with the power of poop.
Zanka got poop on him, Rudo won thanks to poop, and Enjin is having the time of his life. For all that talk about Rudo being a Sphereite, Zanka turns out to be the Ground equivalent of a rich kid who frankly needs to be knocked down a peg, though praise from Enjin can perk him up immediately.
Rudo met Enjin, his savior and intro to the Cleaners, he's met Enjin his trainer/instructor, and now in the back of Enjin's van he's met...Riyo (Yumiri Hanamori!)! A cute and attractive girl who immediately gets in his face and plays with his hair! Lucky Rudo.