Marco Ikusaba is the Seventh diary holder in the survival game, a position he shares with Ai Mikami, the woman he loves. He and Ai grew up as orphans, and their bond formed after Ai was adopted by Kamado Ueshita, who was Marco's guardian. Their devotion to one another is so intense that their primary motivation for participating in the deadly contest is to win and become the god of time and space together, allowing them to live for eternity as a couple. Marco is a skilled street brawler, possessing considerable physical strength and combat instincts that make him a formidable opponent even without his diary. His role in the story is that of an antagonist who clashes with the main protagonist Yukiteru Amano and Yuno Gasai, serving as a test of their ability to overcome a perfectly synchronized team. Together with Ai, he uses their shared Future Diary, the Exchange Diary, which predicts the immediate future of each partner. This allows them to act as a perfect battle couple, covering one another's weaknesses and coordinating attacks with seamless teamwork. Marco also initially wields a fake diary called the Unbeatable Brawler Diary, which predicts his opponent's attack patterns, to mislead others about their true power. Throughout his appearance, Marco remains almost exclusively defined by his relationship with Ai, and his development is tied to their shared goal and eventual fate in the game. He is a physically capable and emotionally devoted character whose strengths lie in his combat ability and unwavering partnership with Ai.