The most obvious of any relationship in Gravitation, the love between Shuichi and Yuki. A huge part of the plot is dedicated to Shuichi's struggle with his work and pursuing Yuki, while Yuki secretly cares for Shuichi but would rather die than admit it. Although Yuki can be a bit manipulative at first, using Shuichi to get rid of his elder sister, Mika. Unsuspectingly, Shuichi had fallen in love with Yuki when he first laid eyes on him. True, Shuichi was first depressed, then mad about Yuki's accusations, but he soon found himself running in front of his car on the street and going over to his house to confront him. Yuki realized Shuichi's attraction before Shuichi knew it himself. It was Yuki who bluntly asked him the question that made him really think. Much of Shuichi's moodiness comes from Yuki's behavior towards him. Shuichi simply can't bare it if Yuki would not speak to him or is mad at him. When Mika told him to persuade Yuki to come home in exchange for Tohma's backup for Bad Luck, part of him may have wanted Tohma's support, but Shuichi also did it to find out more about Yuki and help him. It is Yuki who doesn't understand Shuichi's affection for him in the beginning. He was confused and surprised that Shuichi didn't want money or sex from him, just love. No matter how many times Yuki calls Shuichi an idiot or tells him he has no talent, Yuki's only expressing his affection towards Shuichi. Yuki is the kind of person who uses verbal irony a lot. He would say one thing but would mean the exact opposite. Unfortunately, it took Shuichi 13 episodes to realize this, but if it didn't, Gravi would lose some of its charisma.^_^

In many ways, Shuichi and Yuki help each other through things. In the beginning, it was Yuki who led Shuichi to finish his song so fast, because Shuichi was more determined then ever to finish them just because Yuki had uttered those heartless words. Yuki later gave a lesson to Shuichi on how Seguchi Tohma works. He was approached by Hiro to go and make Shuichi understand that Tohma doesn't do things half-heartedly. Also, he wants Shuichi to understand that a new manager or member is fine, because it will help in making Bad Luck a huge hit. Even if it's not huge, the act of Yuki laying a blanket on Shuichi while he's sleeping is a big step in their relationship. Yuki found it hard to exhibit his affection for the pink-haired boy at first, since his past affections have been rejected. But thank goodness for Shuichi's constant pursuing and his outrageous outbursts (yelling "Yuki's mine!" in the middle of a concert), for it helped Yuki come out of his tightly-shut shell. Even with Mika's warnings that he doesn't know anything about Yuki, or Tohma's threats to stay away from Yuki towards the end, Shuichi refused to stay away and would go great measures to locate or persuade Yuki. He would attempt to disguise himself as a suitcase or dress up as a girl, or stampede across Japan to try to locate Yuki. Finally, Shuichi understands that Yuki means the opposite of what he says, and Yuki understands that Shuichi only wants love and be loved in return. This is how Shuichi is able to reach his goal and shine, with Yuki as well as his friends backing him up, all the way through.