High School Adventures - When Ishizu comes to Japan to work at the museum, Mahad develops a crush on her that he flatly denies. He later comes to terms with it after going out with a crazy teacher of Mana's, and the two kiss and become a couple, with one of their first dates being at the carnival with Ishizu in a yellow one-piece swimsuit.
The Little Dark Magician Girl - When Mana was turned into a human, Mahad was turned human as well by accident. Mahad then develops feelings for Isis that she develops as well. When Isis is killed by Vivian, Mahad gives up his life as a ka to give her back life, and the two officially become a couple.
The Little Dark Magician Girl: Return to the Ka World - Shortly after Atem and Mana got married, Mahad and Isis got married as well, and they had a son named Manar.
Yu-Gi-Oh! Beauty and the Beast (Vase) - Mahad was married to Isis even before Atem's birth even though it's not real clear since they're both rather quiet about it, and is Yugi's father even though Yugi looks nothing like him and, again, they're all rather quiet about the fact. The most obvious moment is after everyone regains their true forms and Isis and Mahad embrace each other in a more-than-just-friends sort of way.
Yu-Gi-Oh! Lion King II: Simba's Pride - Mahad and Isis were friends when they were kids, but quickly didn't see each other for years once their parents interferred. They meet again and fall for each other, which was not part of the plan. Instead of running away with each other, they return to Egypt and earn the Pharaoh's blessing for their relationship.
Yu-Gi-Oh! Quest for Camelot - Mahad and Ishizu were happily married with a child, Mana, before he was killed. Ishizu still looks to her husband's spirit to guide Mana in her journey.