Welcome to the first chapter of Caught Between Worlds! This is, a cross over between YYH and Bleach.
Beginning in the YYH world with the Spirit Detectives and their OC fifth member.

Not that I know yet, Kurama (Maybe Youko) x OC Possibly Ichigo x OC

On with the Show!... Oh... I don't own any character except for Mayoke, of course Everyone else belongs to their respective creators.

Mayoke yawns as she knocks on Kurama's room door as she passes through the Reikai Tantei hallway, how she hates to be used as a messenger, she is starting to think that she has been in the Reikai too long, and that it is time to vanish back into obscurity and the Makai, she then passes the next few doors knocking on each one. Her long tail flicks in her agitation, it seems that Koenma has forgotten that she has finished her probation, as have Kurama and Hiei, and all three of them remain merely because that is what they wish to do, they have nothing to return too really, and no reason to want to return, except Hiei, who continues to threaten that he will leave and never does.

The four boys find Mayoke waiting for them outside Koenma's office, the normally quite cheerful Cat Youkai looks more than annoyed this morning however, being that it is barely even dawn and she rarely gets more than five hours of sleep on a good day, the days when she doesn't get those five she is almost unbearable to work beside, and so her ears are down, her tail flicking back and fore in agitation and her pale icy blue-green eyes are narrowed.
"Ne. Koenma has summoned us all for who knows what reason… He says it's urgent but he's made me wait out here while he finishes something or another…"
"Have you even slept yet, Mayoke-chan?" Yusuke asks, watching Mayoke's tail, which always gives away how she is feeling to some extent.
"Two hours… I may be Youkai, but even I need my sleep" She utters and Yusuke shakes his head a little, then he opens the door and heads right in with the rest of his five man team right behind him and Mayoke hisses angrily when she realises that Koenma is curled up on his chair, fast asleep with his cloak for a blanket and Yusuke smirks as he walks across quietly then glances at everyone and Mayoke, with the most sensitive hearing in the room just crosses her arms and flicks her ears back against her white haired head as he takes a deep breath then yells loudly.
"HOW COME YOU GET TO SLEEP WHEN WE DON'T?!" Koenma leaps up out of his chair, landing on the floor in a teenaged tangle of limbs and Mayoke giggles softly before she nods in some form of satisfaction and her tail finally stills behind her, held with a natural curve, flicking upwards behind her and Koenma glares at Yusuke as he untangles himself from his red cloak and then he gets up slowly.
"What in the name of… Was that for Yusuke?!"
"You get Mayoke-chan to wake us all up for something important and tell her that you have something to do first so that you can sleep after waking all of us up?!"
"Well! Since you are all up!… There's something troubling going on"
"Damn right there is something troubling going on! This Cat Youkai hasn't had enough sleep and she's getting irritable" Mayoke snaps and Hiei almost agrees with her in the respect that he also hasn't had enough sleep, but he is always irritable, whether he gets enough sleep does not seem to affect his moods in the slightest, using his trademark.
"Hn"
"Yes… Well I think you will find this more important… A rift has opened in the Ningenkai… Nothing has come through yet but we have no idea where it leads"
"Obviously not to the Makai or Youkai would have come through long before now… And obviously not to the Reikai or you would know that…"
"Correct… So I want you five to investigate"
"And if it closes behind us?"
"We're running tests to find a way to force it open again if it closes…"
"I'm guessing that this isn't one of those missions you offer us as a courtesy…"
"No. It has to be you five… This is your area, these sorts of things are the precise reason that the Reikai Tantei exist"
"Great… Not only do I not get to sleep. I have now got to travel through some rift when we have no clue where it leads"
"I'll give you two hours to pack some things, but then I expect you all to be ready to leave and you had better not still be complaining"
"Yeah, yeah, whatever" Mayoke utters and she is the first to leave with her tail flicking behind her, only a single flick, contempt for Koenma perhaps, she has never really liked him, and her temper always seems foulest when he is close by, maybe it is just because he is the closest she can get to a cat fight, especially in the Reikai, at least she won't have to hide her ears and tail in the hours just after dawn.
"Why is she always like this with me…"
"You're a wimp and you won't stand up to her" Yusuke states, smirking slightly as he leaves, for a sixteen year old he is even more cocky than he ever was before, learning of his Youkai heritage hadn't stopped that, nor has coming back to work for Koenma when Kurama and Hiei decided not to leave either, only one of them still pretends to be cocky, but actually worries about what may happen around them, he worries about everything.

That's chapter one all done...

Don't worry too much. The next chapter will be up once this one has some reviews... (and I've finished working on it)

Translations:
Reikai Tantei - Spirit Detectives (Of course)
Ne - Hey
Youkai - Demon
Ningenkai - Human World
Reikai - Spirit World
Makai - Demon World