They might start as antagonists. For example, if a mercenary is hired by a dark wizard to capture Harry Potter, they would directly oppose the main character. But sometimes, they can also be reluctant allies. Maybe they are offered a large sum by Dumbledore to protect Hogwarts and end up working with Harry and his friends.
Mercenaries often interact with the main characters in a transactional way. If they are hired by the Order of Phoenix, they will do what they are paid for, like providing security or intelligence. However, they may not always be completely honest or upfront. Their loyalty can be bought, so the main characters, especially the more idealistic ones like Hermione, may be skeptical of them. There could also be situations where a mercenary has a change of heart during the course of the story and becomes more of a true friend to the main characters rather than just a hired hand.
Chapter 444, "Wait and See", is the clearest early answer because it turns Captain's situation into a concrete plot event. It opens with Carrying a backpack, Yu Li walked for over ten minutes but ultimately... and closes on [HAHAHAHA, they're out of luck running into Sister Li!] [Jiang Li is....
Chapter 506, "The Female Devil Can Die", is the clearest early answer because it turns Zhuola's situation into a concrete plot event.
Chapter 754, "Evil Can Never Defeat Justice", is the clearest early answer because it turns Wen Jiaojiao's situation into a concrete plot event.
Look to Chapter 1 for the clearest answer. It begins with Jiang Li, I'm warning you, don't set your sights on Yinwan anymore, or..., keeps building through Following a bout of tinnitus, she struggled to open her eyes and finally..., and lands on Yet before she had the chance to teach her a lesson.
Chapter 402, "The Survival Game Officially Begins!", is the clearest early answer because it turns Shiguang's situation into a concrete plot event. The setup is What kind of face was it?, but the pressure keeps building through Skin cold and white like jade, features delicate as if cast from a....
Chapter 750, "A Complete Beast!", is the clearest early answer because it turns Complete Beast's situation into a concrete plot event. It opens with Shu Yan glanced at Jiang Li with disbelief and then fell into deep...
Chapter 599, "The Weather has Cooled Down, the Merchant Should Go Bankrupt", is the clearest early answer because it turns Dad's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Shang Zhenhe continued, "Shaojing is really out of line, leaving a...
Chapter 516, "Choosing You as an Undercover Agent is Pretty Stupid", is the clearest early answer because it turns Shang Shuyue's situation into a concrete plot event. Early on, Why are you skulking around and observing us?" Jiang Li cut straight....
Chapter 589, "Green Tea! Green Tea! Damn Green Tea!", is the clearest early answer because it turns Mr's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Thinking of this, Zhao Lang gave a slight smile, "Alright, pedaling...
Chapter 683, "This is where you will be filming from now on!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with The Capital had entered winter by November.