Happy Together is not a pure Yunjae fanfic; the main couple is in fact Yoosu, however Yunjae and Changmin all play huge roles in the fic (I'd say the fic is 50% Yoosu, 40% Yunjae and 10% Changmin- Changmin also comes out alot in the Yoosu portions of the fic). The author of Happy Together is Manish, who is another very highly regarded writer in the Korean DBSG community- she mostly likes writing Yoochun-uke fics so she writes a lot of Ahki (Junsu x Yoochun) and Woongki (Jaejoong x Yoochun), which was why I never really read her fics even though she is a famous writer- I'm really an only Yunjae type of person. Also, to me Yoochun is seme- I mean in 2u (Yunho x Yoochun) and Seuki(Changmin x Yoochun) I can see him being uke but being uke to Junsu and Jaejoong?!? XD;; Anyways, I will reiterate- every single DBSG fanfic recommendation site, you will see Happy Together being highly recommended. And it's really easy to see why.
Happy Together was the first (and only to my knowledge) Yoosu/Yunjae fic that Manish wrote and omg I love her for writing it. Finishing up at 589 pages, it is pretty damn long however I can safely say that this fic was so interesting and well written that I just couldn't stop reading it. It is an epic of a mafia fic. The Yunjae in this story was just so wonderful- there was definitely not as much Yunjae as there was Yoosu; however Yunjae just stole the show. BTW if you plan on reading this fic, don't read anything else because I will spoil it for you. If you can read Korean, get the hell out of here and read Happy Together!
Ok so about the fic- all five characters play huge roles.
Changmin- he's a famous prosecutor. Once he takes a case he won't rest until it's over. He is the oldest among the five and he was engaged to a woman several years ago until a tragedy occurred. I think his side story is the smallest but it was still interesting to read.
Yoochun- he's a detective who works with Changmin. Young and brash, he tends to act before thinking but his heart's in the right place.
Junsu- a party planner. He sleepwalks during the night if he does not tie himself down to the bed...
Jaejoong- a law school student. He is regarded as a genius amongst his peers.
Yunho- a mafia boss who came to Korea from New York. The mafia name is K cartel and is very advanced and different from other Korean mafias. Because the members are all illegal immigrants, they don't exist in records (all the members of the mafia are extremely loyal because the K cartel helped illegal immigrants in NY).
Ok I'm not going to mention that much of Yoosu except for the really important parts because really my main focus is Yunjae XD;
Jaejoong's father is a gambler and a drunk- he borrows money from Yunho's mafia to fund his gambling and doesn't pay them back. They kidnap Jaejoong and force him to agree to become their lawyer (at this point Yunho is pretending to be the right hand man of the 'boss'. Yunho had already fallen in love with Jaejoong a long time ago- I'll get into that later. The money that Jaejoong's father owed the mafia is just a scheme to keep Jaejoong by his side). Jaejoong slowly starts liking Yunho (who makes it pretty obvious that he's attracted to Jaejoong). Yunho is kinda stalkerish in this fic- but not in a scary ass way (I adore Yunho's character in this fic. He's so HOT). Like Jaejoong has a girlfriend (this is near the beginning of the fic, like right after Yunho brings him into the mafia) and Jae's kissing her but he's feeling all weird because he and Yunho kissed earlier and he liked it. So he's kissing his girlfriend but feels nothing and he's like 'what's wrong with me?!' Then he sees Yunho standing there in the shadows watching them and Jae is just like 'holy shit!!'
I heart jealous and possessive Yunho, I really do.
Ok so I'm going to explain Yunho (because really at this point he seems very stalker-ish yes?). Yunho was a mafia boss in NY and he really fell for Jae at first sight in NY. You see, Jaejoong used to play piano in NY for recitals. Yunho attended every single recital that Jaejoong performed but never spoke to him (just admired from afar). So one day Yunho decides to give Jaejoong flowers along with a card asking Jae to meet him outside. Yunho gave Jaejoong the flowers but there were so many reporters and people hounding Jae (giving him more flowers and stuff) that the card accidentally dropped on the floor. So Jaejoong never read the card. Yunho just waited there for a long time and thinks to himself that Jaejoong is not coming. So he decides that next recital, he will ask Jaejoong directly. But Jaejoong never comes back to NY (his dad is a gambler and wasted all their money so he quit piano). The main reason that Yunho decides to go back to Korea is to find Jaejoong (other reason is he wants to control drug and firearm trade in Korea).
Anyways while all this cute, fluffy stuff is going on, we also see the mafia boss Yunho. He's cold and cruel, killing his enemies without remorse (he plans on controlling drug/firearm trade in Korea so he's been threatening the leaders of the other Korean mafias and forcing them to acknowledge that- the ones that don't, he kills). Anyways, Jaejoong finds out that Yunho is actually the leader of K cartel and Jae becomes really really angry with Yunho and the two have a huge fight.
*will edit and write more later ~_~