Yu-yu Kondo starts as a shy third-year junior high student in Kanazawa City, Kaga Province, possessing the ability to perceive others' emotions. This sensitivity makes self-assertion difficult, leaving him vulnerable to manipulation, especially by his older sisters who force him into cross-dressing for their amusement. Dressed in a honey-blonde wig, vintage dresses, or a Raika Academy female uniform, he often appears strikingly attractive, causing him discomfort. His standard attire is a green and white jacket, black jeans, and brown lace-up boots, later changing to a cropped red and black jacket with red zip-up boots in high school. He has short dark blue hair, fair skin, and purple eyes.

His life shifts when Megumi Okura invites him to Wonder Hill, an abandoned amusement park. There, he witnesses a Vanguard cardfight between Team Blackout's leader Danji Momoyama and the formidable Tohya Ebata, drawing him into the game and sparking personal growth. Initially stammering and reserved, Yu-yu gains confidence through Vanguard and joining Team Blackout. His early resilience surfaces when he fiercely defends the team's banner against Tohya during Danji's absence. His emotion-perception ability becomes crucial in key conflicts, such as breaking through Mirei Minae's emotional barriers at Nagoya Castle by understanding her inner turmoil.

In will+Dress, Yu-yu becomes Team Blackout's leader after Tohya departs. Now a high school student attending the same school as rival Raika Koshiba, he shoulders greater responsibility. His leadership faces tests during the Vanguard DELUXE tournament and the rise of the Uniformers, a group advocating abandoning individuality for strength. His opposition to their ideology turns self-righteous, driving an obsessive quest to defeat them and "save" former ally Zakusa. This arrogance culminates in a loss to Zakusa (now Shirogane), forcing Yu-yu to confront his own hypocrisy. Recognizing his flawed approach, he undergoes significant humility and recalibrates his view of strength and identity. His Dragon Empire deck mechanics evolve alongside this journey: starting with overDress (evolving Trickstar into Vairina variants), progressing to X-overDress (combining Trickstar with Prayer Dragons), and eventually integrating both mechanics, symbolizing his acceptance of past and present growth.

Yu-yu achieves a pivotal victory over Uniformer leader Gui, reaching mutual understanding. This triumph solidifies his belief in individuality and authentic strength. He subsequently passes leadership of Team Blackout to Megumi Okura and departs Wonder Hill to embark on solo travels, seeking to explore unseen worlds and broaden his horizons. His journey concludes with the leadership transition, reflecting his transformation from a hesitant follower into a self-assured individual valuing personal connections and continuous growth.