To level up your World Tour character quickly in Street Fighter 6, here’s a detailed guide that incorporates various strategies for maximum efficiency:

1. Engage with Stronger Opponents and Unique Citizens
Challenging stronger opponents and unique NPCs, especially those adorned with distinctive costumes, can significantly boost your experience points (XP). These special characters are typically found in areas like Beat Square in Metro City. Target them for battles, as they tend to provide more XP than regular NPCs, making each fight not just a challenge but a rewarding experience.

2. Participate in Tournaments at Haggar Stadium
Tournaments are a goldmine for XP and Master EXP. At Haggar Stadium, you can enter daily tournaments that offer consistent experience rewards. Additionally, normal tournaments can be repeated infinitely, providing continuous opportunities for leveling up your character. As you progress and reach Master Style level 20, you’ll unlock daily sparring sessions with Masters, which offer substantial XP boosts and help refine your skills further.

3. Complete Missions and Side Quests
Embark on missions and side quests scattered throughout the World Tour mode. Completing these objectives can rapidly enhance your level progression. Keep an eye out for elite bosses and other mission targets that are designed to provide notable experience gains. Engaging in both combat-focused and exploration-related activities broadens your experience earning potential.

4. Build Relationships with Masters
Fostering relationships with Masters is essential. The more you utilize their fighting styles and special moves in matches, the more Style EXP you’ll earn. This not only allows you to unlock new skills but also brings bonuses that enhance combat performance, making your character a more formidable opponent.

5. Utilize Supplements and Upgrades
Maximize your combat effectiveness by strategically using supplements and skill upgrades. When distributing Skill Points, prioritize enhancements that augment combat attributes rather than merely focusing on World Tour benefits. This approach ensures that your character is well-rounded in fights, giving you an edge over opponents.

6. Explore and Use Master Actions
Master Actions are vital for navigating Metro City and unlocking hidden areas filled with valuable items and experience. Familiarize yourself with these actions and employ them to access previously unreachable locations. Discovering these areas will not only reward you with experience but also enrich your overall gameplay experience.

Conclusion
By combining these strategies—fighting unique NPCs, participating in tournaments, completing diverse missions, building relationships with Masters, utilizing skill upgrades, and exploring with Master Actions—you can efficiently level up your character in the World Tour mode of Street Fighter 6. Focus on these aspects to enhance both your gaming experience and the performance of your character in battles.