Yuri Shibuya was a normal fifteen year old baseball loving high school student in Japan until the day he was flushed into an alternate universe by some bullies. He was trying to protect his friend when the guys turned on him and shoved his head into a toilet. He woke up and thought that he was in a theme park, as everyone was wearing strange clothes and talking about odd things. The people, especially one man named Adelbert, wanted to do him harm because of his black hair and black eyes. Before he could sort out everything that was going on, he was rescued by two men named Conrad and Günter. They called him 'your majesty' and brought him to a castle. They explained to him that they were of the Demon Tribe and that he was their Demon King.
Wolfram was the youngest son of the former Demon Queen, Lady Celi. He was a spoiled brat and did not think that Yuri was a suitable king for their land. He even went as far as to insult Yuri's mother over dinner. Yuri took great offense to this and slapped Wolfram across his left cheek. Everyone told him to take it back, but Wolfram had insulted his mother and Yuri said that he wouldn't take it back ever. Congratulations started flying at once, and Yuri learned that he had just asked for Wolfram's hand in marriage by slapping his cheek. Wolfram was so embarrassed and infuriated and so challenged Yuri to a duel to take place the next morning.
After Yuri bested Wolfram in the duel by using his awesome Demon King powers, Wolfram warmed up to the idea that they were engaged. He took to accompanying Yuri on all of his travels to prevent anything inappropriate from happening and became extremely jealous of everyone. If Yuri so much as talked to another (male or female), Wolfram would grab him in a headlock and remind him of their engagement. Yuri wanted to break it off, but Wolfram was too proud to do so, and he actually started to like Yuri. Yuri saw their relationship as a friendship, but Wolfram saw it as more.
One of the running storylines dealing with their relationship was the fact that Wolfram slept in Yuri's bed. Yuri was really freaked out one night when he found Wolfram sleeping next to him in a frilly pink nightgown and never got used to it. When he kicked him out of his room, Wolfram found a way back in. Wolfram believed that since he was Yuri's fiance, he didn't have to ask permission to sleep in his room. Yuri tried to find Wolfram another place to sleep one time, but that ended with the two becoming"parents" to a swarm of bear-bees and Wolfram right back in Yuri's room.
Yuri always bounced back and forth between Japan and the Demon Kingdom, and Wolfram didn't appreciate this fact. He also didn't understand why Yuri didn't spend all of his time with him when he was back because they didn't know how long his stay would last each time. Yuri was not very comfortable with Wolfram's possessiveness at first, but came to appreciate his company. The two became good friends and Yuri began to accept the engagement as fact over time. He might not have loved Wolfram as Wolfram loved him, but both were very protective of one another and would do anything to keep them from harm.
While Yuri is still not comfortable with his and Wolfram's "situation", he has stopped debating it. I think that he still views them as just friends, but there is the possibility that he will feel more for Wolfram in the future (taking into account the fact that Wolfram won't let him even look at another person without questioning his faithfulness). Yuri adopted a little girl named Greta, and Wolfram is already treating her as his daughter as well. The two young men are adorable together and both have helped the other mature a lot over the course of the show. Wolfram may still call Yuri a wimp, but he doesn't seem to mean it as much of an insult anymore, and Yuri seems to know that.
I don't think that their relationship will progress to any greater heights throughout the rest of the show, but that is okay because Yuri and Wolfram are cute enough. Wolfram did meet Yuri's parents and both seemed more than all right with their son's situation. Yuri's mother just adores Wolfram and even suggested taking him shopping for a wedding dress. The show isn't really one that I can see showcasing a mature relationship though, so we'll just have to take it and accept that what Yuri and Wolfram have now is probably all that we're going to get.
This scene is from the episode "Sailors and a Spoiled Brat". Yuri went down to the dance on the ship and asked a little girl to dance with him. When he got back to his cabin, Wolfram was ready with the jealous fiancé routine.
Wolfram: "You big double crosser!"
Yuri: "What is this? Why all of the sudden are you calling me a double crosser?"
Wolfram: "Because you're a double crossing traitor! How could you do it, dance with a woman behind my back?"
Yuri: "Oh my goodness."
Wolfram: "Now listen! You think you're cute, and maybe you actually are, but being cute doesn't make it okay for you to be unfaithful!"
From the same episode, the ship they were on was being attacked by pirates. Yuri and Wolfram were told to hide in the closet and both were a little worried about what was going to happen if they were found.
Wolfram: "Now listen, if the pirates find me you mustn't resist them too much."
Wolfram: "They won't want to take your life away because you're too good looking to kill."
Yuri: "Well you'd better not fight them either! You're a gazillion times cuter than me anyway."
This quote is from the episode "Rainfall in the Desert". Yuri had been missing with Wolfram's older brother Gwendel and rumors had been flying that they had eloped. When he was finally found, Yuri decided to ride on the back of Conrad's horse (Conrad is Wolfram's other older brother). Being Wolfram, he was extremely jealous of this fact.
Wolfram: "Yuri, why in hell's name aren't you riding with me on my horse?"
Yuri: "Well, I can't say I've given it any thought."
Wolfram: "Thinking isn't your specialty, is it? Surely you haven't forgotten who you're betrothed to?"
Yuri: "How could I?"
Wolfram: "Sicko, insensitive... you're always like this! I hear slanderous tales about how I'm the fool who had his fiancé stolen away from him by his big brother."
This quote is from the episode "The Past and Future". Yuri had just been given permission to adopt a little girl named Greta and Wolfram volunteered to prepare the reception.
Yuri: "Thanks Wolfram, you've made Greta really happy. I had no idea that you liked kids so much."
Wolfram: "Hey, I'm not an idiot. If you become Greta's father, that means that I - as your fiancé - will also someday become a father. We'll be a normal two-parent family. What's so wrong about showing affection to one's own daughter?"
Yuri: "How did she suddenly get two fathers?"
Yuri had been missing for quite some time before the episode "The Ends of the Earth." Wolfram was sick with worry for him and set out to find him. He ended up getting to Yuri just in time, as he was about to fall into a gaping hole that formed in the ground just moments before.
Wolfram: "Finally, I caught you!"
Yuri: "Wolfram, what are you doing here?"
Wolfram: "Well Yuri, since you're such a little flirt, I put a transmitter on you so I could track you down the world over. Come on, I'm lifting you up."
Yuri: "One false move and you'll fall too."
Wolfram (smiles): "In that case, we'll just fall together."