Yang and Mercury first met in volume 2 when him, Cinder and Emerald posed as students from Haven Academy, pretending to be there for the vytal festival tournament. Yang was also watching in the audience when he fought against Pyrrha Nikos. He then fought alongside Yang and many other students when the grimm invaded Vale.
In volume 3 Yang asks Emerald if her and her team wanna hang out but then when she sees Mercury smelling the inside of a boot she quickly changes her mind. Later in chapter 7 Yang and Mercury are selected to fight against each other in the singles round. Before the match starts Yang tells Mercury he better not go easy on her to which he smugly responds with "you wish". After the fight is over Yang tells Mercury better luck next time, to which he responds "There's not going to be a next time Blondie". Yang then turns around and sees an illusion of Mercury about to attack her so she fires a warning shot at his legs. The crowd immediately starts booing and Yang is immediately surrounded by guards. She then sees herself on a screen attacking a seemingly defensless Mercury for no reason. He then yells at Yang and asks why she would do that him. He's then taken off to an ambulance and Yang is disqualified from the rest of the tournament.
In volume 5 during the fight at Haven academy Yang primarily fought against Mercury. At some point during the fight he knocked her down and then Emerald used her semblance on Yang to make her think she was seeing multiple duplicates of him. Ruby then told Yang to go after her mom and Cinder once they left the battlefield. Mercury tried to stop her by grabbing her arm and Yang did get angry and looked like she would activate her semblance as her eyes turned red but then decided against it and ejected her fake arm. She then proceeds to run after Raven and Cinder armless while Mercury is left standing there holding her prosthetic arm.
Combat Boots is a rarepair within the RWBY fandom. While it's fanbase is small, many who don't necessarily ship Combat Boots still like the idea of enemies turned to lovers. Also now that it's been proven that Mercury is having second thoughts about Salem, there's a chance he might betray her and join the heroes side. They both also have similar fighting styles, as they're both close range fighters. They both also now have prosthetic limbs for their missing body parts.
- Their ship name comes from Yang being the combat fighter, and Mercury being the Boots since he has prosthetic legs and dust infused in his boots.