These are the relationships of Ronin.
Ronin first encountered them in an unseen adventure between the fourth and fifth seasons. The exact circumstances are unknown, aside from them being enemies. He met them again in Stiix, and he ending up conning them into giving him a share of their tea shop. The Ninja were upset by Ronin's actions but didn't mind staying as he proved to help. When Morro and the other ghosts force Ronin to steal the Sword of Sanctuary, he was reluctant but carried out his assignment to save himself. He was forced to escape from them and deliver the item as promised. After he repaid his debts to the ghosts, he allowed the Ninja to use R.E.X. as a way of apologizing for his betrayal.
In Season 6: Skybound, Ronin hunts the Ninja for their bounties after they are framed by Nadakhan. Ronin did question their supposed turn to villainy but wanted to receive compensation and used his knowledge of their skill to capture them. After receiving his fortune, he later helped Jay by joining the Ninja Replacements to save the ninja. Because of Jay's wish, this was undone.
During Day of the Departed, Ronin helps Jay by saving his parents from a resurrected Samukai even though he tried to steal from them. In the end, he was rewarded with scrap and told he only had to ask.
During Season 9: Hunted, Ronin was imprisoned because of his past affiliation with the Ninja by the Sons of Garmadon. Ronin did not have too much faith in Lloyd freeing the city as the latter's mother did. In Green Destiny, he overheard the ninja returned and broke out to help them in freeing the city. Ronin aided the ninja in defeating the Colossus by chaining it down. After Garmadon was defeated, Ronin can be seen in the audience of citizens who cheering on the ninja for saving them.
In Season 5: Possession, Ronin met Nya when her friends accidentally gave him a share of their tea shop. Ronin didn't mind telling Nya he was in debt to the Soul Archer and helped Nya with her training by giving her advice of not caring too much, which somewhat help. When Morro and the other ghosts force Ronin to steal the Sword of Sanctuary, she impedes him, forcing him to fight her since he needed to repay his debts to the ghosts.
During the fight, she sees a future of him kissing her, which causes her to kick him in the leg in disgust as he questioned it but she replies he knows what he was going to do before he takes the sword from her. She is disappointed when he hands it over to Morro but is relieved when he helps them fight the Preeminent.
They still gets along with and may see each other as friends, even if Nya is still put off by his thievery.
During Season 9: Hunted, Ronin was imprisoned because of his close affiliation with the Nya and the other ninja. After he learns the other ninja returned in Green Destiny, he breaks out and heads to help Nya and the others in defeating the Colossus by chaining it down. While they don't interact, Ronin cheered for her after they were honored as heroes.
The two barely interact but appear to be on good terms as Dareth goes to him for trophies for achievements he hasn't earn to make himself look good.
In Season 7: The Hands of Time, Dareth ends up breaking Ronin's leg though he apologizes for his blunder and tends to him to make up for it. Ronin was irritated by his act though didn't appear to be too angry as he allowed the latter to care for him as a way to make up for it.
Ronin was in debt to him and had to pay him, otherwise his soul would be sent to the Cursed Realm.
Eventually, Soul Archer's ally Morro used this to the ghost warrior's advantage by altering the deal with taking the Sword of Sanctuary. Ronin was reluctant but ultimately betrayed the ninja and handed over the blade, concluding their deal.
It is shown in "Firstbourne," Ronin and countless civilians of Ninjago affiliated with the Ninja were arrested.
During "Green Destiny," Ronin overhears them say that the Ninja returned and broke out to aid them. Afterwards, he personally taunts the defeated cult on their predicament, in revenge for them having him locked away.