I was reading Black Dragon's story millennium and this idea popped into my head.
Having a real enemy for Ranma provides purpose as well as motivation. Ranma's abilities will be based on high end feats in the manga. Ranma will learn new techniques, copy techniques he seen (especially if he's seen them often meaning he will definitely know breaking point, Happosai firework technique, and hidden weapons) as well as improve existing ones (new variations on ki blast, hiryu shoten ha, etc.). He will also use magical items. Some would think that this is making Ranma god-like I don't really see it that way, in my opinion this isn't making him anymore god-like than he was in the manga.
Ranma 3 months post manga just started 11th grade (age of Ranma for the fic would be 16 since Ranma's age is not said until mushrooms of aging story arc and he says that he'll lose 1 year instead of saying 3 months or something like that I'm assuming that Ranma turned 16 shortly before that story arc).
As of yet unnamed and unwritten Ranma/Hellsing/other crossover (considering all the thought I put into this idea I hope I do write it, instead of getting fed up and quitting like I've done with all the stories I started in the past)
Only thing taken from Hellsing is the vampires. The other hasn't been decided or known yet and may end up being an original character. I want to set Ranma up with a girl who is nicer than his fiancee's and can help him but also won't get in his way/distract him while he's fighting. The reason I feel a need to add a girl to this is to help balance the fic out. I don't want this to be an all dark angst depressing fic. The Ranma cast don't really fit with what I'm looking for. I'm not exactly sure what I'm looking for in the girl. She has to be someone who Ranma can talk to and trust. A person who he can open up to without fear of what he tells her being used against him later (though the opening up part will be slow going since Ranma doesn't really tell anyone anything unless he has to and for good reason)and who shows that she trusts him. I don't want her to be helpless (leads to lois lane syndrome, e.g. superman help), I also don't want her to be too powerful (no point in Ranma's battles if she can simply defeat the beings he's fighting). I'd like her to help him accept his female form, show him that the way the people around him treat him is not normal (e.g. hitting him, using him as a scape goat, blackmailing him, etc.), and for her to have little modesty around Ranma figuring there is no point to it since he's not only seen everything, he has everything she does. Little modesty part is so I can use her flashing, mooning him, etc., as part of his training. In the manga Ranma is far to easily distracted in fights which could lead him to getting killed, look at the manga the reason Mariko knocked him out was because he was to busy denying his love of Akane to pay attention to her, the reason Kuno was able to hit him was because he was looking at pictures instead of paying attention to Kuno, and he was too busy arguing with Akane to pay attention to Ryoga almost getting Akane killed. Also she won't live in Nerima she'll be someone/somewhere Ranma goes when he wants to get away from Nerima for a little bit and Ranma will have an easier time opening up to her because he won't see her as a love interest just a friend.
Here's the main fic idea the part with the girl would be a subplot.
People are being slaughtered in Tokyo. Ranma's nature is to help people if he can so he isn't about to stand idly by while people are being killed. Ranma manages to find the killer, who happens to be a vampire of the Hellsing universe variety. Doesn't know it's a vampire thinks it is just a martial artist who's gone serial killer though Ranma's danger sense is going crazy. Ranma's normal fighting style and lack of knowledge on how to fight vampires (as well as not knowing it is a vampire) causes Ranma to make several mistakes that are in character for him. First he's going to underestimate the vampires abilities (strength, speed, durability). Second he's going to try and take down the vampire without killing or maiming it. Thirdly he's going to be wasting time and energy showing off, taunting it, and playing with it. Suffice it to say Ranma's not going to win this confrontation but will manage to get away.
Genma and Ranma will have a talk about the fight. Genma is going to tell Ranma that there are times when you have to kill. This person has gone to far and slaughtered people. The police won't be able to keep him arrested. Genma will make the decision to give Ranma some scrolls containing the Umisenken and Yamasenken (with new stuff added since he had made the original one Ryu had). Mentions that Ranma can be trusted to use them responsibly.
Next confrontation with the Vampire; Ranma is a lot more serious doesn't taunt or play with it. Even though Ranma knows intellectually that he has to kill it (a hard choice that Ranma spends considerable time thinking about his options ultimately agrees with Genma that the murderer has to be taken down) he is still reluctant to kill it and still holds back (e.g. doesn't use Yamasenken techniques or other ki techniques) and gives the vampire a fair chance (e.g. doesn't try to sniper it, sneak attack it, use explosives, etc.). Ranma loses this battle as well though he does manage to escape.
Next confrontation: Ranma is learning from his mistakes so this time he goes in hard and fast using techniques that should kill anything human. He again makes the mistake of giving the vampire a sporting chance i.e. no sneak attack, sniper attack, etc. This is where Ranma learns that it's not human though he still doesn't know that it is a vampire. Having used techniques that should have killed anything human Ranma is completely caught off guard when it doesn't die and retaliates. Since he is caught off guard the vampire is going to hurt Ranma enough that Ranma is going to have to run away again.
After the last fight the Vampire is going to start seeing Ranma as a real threat as opposed to an interesting diversion. Ranma of course is getting pretty fed up he lost against this opponent 3 times as well as angry at himself for not taking down this mass murder as well as feeling guilty for the deaths he didn't prevent. He's also a little afraid but his fear is over shadowed by his guilt and anger.
Next confrontation Ranma is no longer going to give it anything like a fair fight. Sneak attack knives in every vital place on a human followed by using techniques that tear the vampire into little pieces. Ranma is pretty damn sure that that is going to kill it. This being a fairly powerful vampire with the ability to regenerate similar to Alucard's. It doesn't die. While Ranma is watching the pile of blood and pieces of flesh (Ranma is being cautious) he is attacked by a ghoul. This is where Ranma first encounters the Ghouls. A regenerating monster of some type is one thing a small army of zombies is another thing entirely. Ranma fights the ghouls kicking the crap out of them a small army of unarmed zombies isn't going to be able to stop Ranma but it will freak him out and give the vampire time to regenerate and surprise attack Ranma. Ranma is forced to flee yet again.
Ranma goes to Cologne for help. Would have gone earlier but she had to return to China for some reason I haven't come up with yet. Cologne recognizes the being as a vampire by Ranma's descriptions of it and helps Ranma by giving him some magical items to help in his fight (dragon scale armor similar to the armor occasionally worn by Shampoo and the armor worn by Herb, a magical weapon that could hurt it more than physical attacks can - mentions that silver could be used but silver doesn't really make good weapons and that blessed objects could work as well but you have to have faith or the deities blessing for them to work). Amazons have had dealings with vampires before though not in recent years (as in the last century).
That's all I have for an idea so far. Not completely thought out. Other things that probably would happen would be Ranma stealing all the magic things and books Happosai's got. Using water proof soap as a means to control his curse. Training to get better. Seeking out magical items and stealing them or using his feminine charms to get. Ranma reading in libraries on thing like Combat tactics, History, Strategy, Forensics, Psychology, More myth and lore, and other things that he thinks will be of use or someone else suggest to make him better at fighting Vampires. Eventually having a run in with vampires who use modern weaponry.
------------------------------------------ added later
Having just reread this idea it occurs to me that I had made Ranma choose to kill the vampire too quickly. It maybe true that the police would be incapable of keeping a martial artist of the vampire's abilities that Ranma just sees as a psycho incarcerated. Ranma is much more likely to maim the killer than try for a kill so I'll probably end up changing that to Ranma accidentally using a technique that would/should kill a human while trying to maim the vampire after all the police should be able to keep a sufficiently maimed martial artist incarcerated.
************************************* added even later
Still thinking and expanding this idea. It occurs to me that the girl in this fic could be Hotaru (sailor Saturn). While I'd usually consider her to be too powerful (planet destroying) it could work. She has experience fighting inhuman creatures. While she is powerful she, at least for this fic, can be forced to not use her silence glaive surprise attack by having the villain use innocents people around him i.e. as shields and she's not going to destroy the world (to many deaths and where would she live). She doesn't have the speed or strength to get right up and fight in close combat nor the skill (at least not against these opponents her speed and strength would be boosted in senshi form but I figure closer to Akane's level rather than Ranma's judging by anime senshi). Her healing ability would be very useful as well as her ability to create a shield. The shield would mean that Ranma doesn't have to worry about her and that she can shield innocent by standards allowing Ranma not to worry about them. Also if all else fails she can just nuke the entire area but would be a last resort type thing.
While mowing the lawn and thinking about this fic it came to me that I have a problem that I'm unsure of how to solve. Problem being how do I keep the other cast members out of the fights? Sure one or two fights is easy enough to explain but eventually the others will join in or go hunting by themselves. I don't want that. The other cast members could be extremely helpful heck Akane could even take on a bunch of the ghouls by herself. Happosai and Cologne have to be prevented from fighting because they are too powerful/skillful. The other Ranma cast members really aren't very good at working together so will get in each others way, would be distractions in the fight (Akane has been a distraction in several of his fights either because Ranma would be worrying about them, end up fighting them as well, or just get in his way), may see the fight as a way to get rid of one of the rivals without getting blamed for it (Shampoo tried this in manga), could be used as hostages/meat shields, and could be turned into vampires and used against him (this also happened sort of in the manga Akane's form was used by Kima and body was used by spirit doll).
If I choose Saturn as the girl then that brings in the other senshi. Which I also don't want getting in the fights. Sure they have better team work than the Ranma cast (the inners do at least outers not so good at team work), some of the reasons I don't want the Ranma cast involved are the same reason's I don't want the senshi involved, they suck at tactics (just look at their fights in the anime really poor tactics most of the time but since their enemies had poor tactics most of the time this didn't really matter killing Saturn was a real dumb move), their fighting style conflicts with Ranma's (Ranma is far more dangerous up close than from a distance and they are far more dangerous from a distance than up close), they rely more on power and number advantage than on skill (usually was multiple senshi versus one monster of the day with the monster of the day winning until Tuxedo Kamen showed up distracting the monster and giving Moon the time to do her big technique and kill it - her technique is not instantaneous Eudial was able to walk over to her van and take out her weapon while Sailormoon was readying/charging up her attack) against a sufficiently faster opponent like the vampires she won't have the time to power up her techniques before she is gutted unless she starts very far away.