timeline - yuu's storyAll the following information is based on the manga version of Marmalade Boy unless stated otherwise. There are many UNMARKED SPOILERS so please be careful while reading!
→ Yuu believes that his "father" is not his real father based on a letter he finds. He is on the search for who he believes is his real dad.
→ Yuu lives a normal life, dating a girl named Arimi because she asks him to date her for three months to see if she can change Yuu's mind on dating girls. After three months, he politely ends it, saying he is better off alone.
→ The Matsuuras and the Koishikawas meet for dinner to discuss how the parents want to switch partners. Yuu and Miki get into an argument because Yuu tells Miki to allow their parents to be happy and switch. The parents announce that they plan on buying a large house for the 6 of them to live in. Yuu tells Miki to give up and deal with the switch.
→ Yuu and Miki go to the supermarket together. Yuu tells Miki that he thinks they should be friends, but pranks her by putting gum in her hand.
→ Yuu switches to Toryo High School because it is closer to his new home. Yuu is extremely well liked at his new school by both the boys and girls. Girls find him to be extremely handsome.
→ Yuu introduces himself on the morning announcements, and tells everyone that he is living with Miki. Miki gets angry and runs into the production room and explains that they are just family friends living together. She then asks him why he doesn't join a club in which he states that they are too time consuming for him.
→ Yuu decides to skip his 5th period and wanders into the library. Here we find out that he really enjoys reading and books. He then goes to gym class and kicks butt in basketball, too. After Miki gets hit in the face with the ball, Yuu visits her in the infirmary. He asks her if she is awake, and when she doesn't respond, he leans down and kisses her on the lips and then leaves.
→ Yuu and Miki enjoy breakfast together. She asks him to pass the apricot jam, in which he tells her the only thing left is marmalade. Miki laughs and announces that Yuu is just like Marmalade because "even though [he] actually [has] some awfully bitter points, unknowingly everyone's being deceived by the sweetness on the surface." Yuu responds back by calling her mustard girl.
→ Yuu decides to spend some time at the library over summer vacation. He runs into Meiko. They spend some time talking about how they both love the atmosphere of the library.
→ Yuu's mom brings home amusement park tickets from work. Miki and Yuu go and have a great time. Yuu is grabbed by an old girl friend named Arimi. She tells him that she is planning on dumping her new boyfriend now that she has seen Yuu again.
→ Yuu unwillingly joins the tennis team at his new school because one of the players gets really hurt.
→ Yuu and the school president, Miwa, believe that they are truly brothers and that his father, a famous architect, was the real father to Yuu. Mr. Satoashi explains that he could not be Yuu's real father because he never had sex with Yuu's mother.
→ Yuu has a mental break down and cries in Miki's arms because he is so stressed about not knowing who his real father is. Yuu and Miki have a huge heart to heart about how Yuu has purpose even if that truly isn't his dad. Yuu tells Miki he loves her, and she tells him back. They end up kissing on the beach together.
→ Yuu dresses up as a female in a commercial for perfume for his mothers company. A young girl model has a huge crush on Yuu, but only because she likes "cute" things, and Yuu looks cute as a Queen.
→ Yuu finds a photograph of his parents and Miki's parents in a box in the attic. He freaks out because he thinks that his real dad must be Miki's dad and that his mom cheated. He tells Miki he no longer has feelings for her, and ends everything. (This is clearly a lie, he just thinks that she is now his biological sister)
→ Yuu and Miwa talk about the situation. Miwa suggests that Yuu tell his family what he saw, but Yuu wants to hold the burden by himself.
→ Yuu decides to go away to school. Later on, Miki shows up out of the blue to visit him. Yuu is walking with another girl who he tells Miki is his new girlfriend and for her to go away. Yuu lies, the girl is not his new girlfriend.
→ When Yuu comes home for summer break, Miki and him break down and he finally tells her why they cant be together. They go on one last trip to have some time together as they once were. Yuu tells her at the end of the trip that he wants her to endure the pain with him and get married. They go home and confront the family. Yuu's father slaps him in the face for ever thinking that he wasn't his true father. They explain the misunderstanding. Yuu and Miki are able to love each other.