How do you get McCartney in Fire Emblem?

In Fire Emblem: Three Houses, you can recruit the character McCartney by speaking to him during the "Cyril's Side Quest" in the Blue Lions route. Ensure you have a high support level with Cyril, as it will increase your chances of recruiting McCartney. Additionally, completing specific side quests and building relationships with other characters may also influence your ability to recruit him. Make sure to engage with the story and character interactions to unlock his potential.