What's His Story?

Okay I've been wrestling with this for a week now so here I am, asking for help.

I have two main characters: a half-brother and sister.. They share a dad.

The girl's story is set. Her mother was a queen, her dad is magical. She's on a quest and there's a faction after her.

The boy's story is unclear. He's important to the story. I know his ending and how he grows, but he needs to have some storyline to GET there.

He doesn't know his mum and his dad has been MIA for ten years (they will all meet but not yet!). Currently he's trying to find his sister after she ran away. But he needs some deeper journey he's on or somethign else he's also seeking/experiencing.
At the moment I'm writing scenes which could be summed up as "he walked through the streets, asking in the inn, then travelled on through to the next village". There's a lot of conflict between him and the faction later but he's not aware of them yet. I just need to give him some subplot or introduce conflict thats not bandits attack or there are mines in the road as i've done those :P

He's 19 and works as a city guard (though is currently just a boy on leave travelling east through towns/villages asking for his sister). He will eventually learn that he has magic and meet his father in a couple of chapters but the girl needs to get to a certain space first and i just need to.. kind of tide him over.

I've had a look in the adopt a subplot forums and didnt see anything that could match. Any ideas would be awesome.

So you need a subplot? Often when people ask for a subplot, I suggest a love story. But I don't think that'll work here. Adding a whole new character would really shake things up and I don't think you need that. I would say that you should have him rescue a damsel in distress. That's always a classic. Or alternately, you could have nothing happen to him. Just skip time, or focus on the half-sister for a couple of chapters and pick up his story when he discovers he's got magic. You don't have to stick with him the whole time.

Does anyone else have any suggestions?

I'm sorry, I just don't see why you cant' move his story forward. if you insist on doing a chapter for each viewpoint like that, you're limiting yourself and forcing yourself to write something you can't even think of for yourself. they are in completely different places I assume, so the only way their plots connect is that they are siblings (and he's trying to find her, but shush) the question is, why does he need to wait for her when its obvious he needs to move on?

Also, is he travelling alone? because of course that's going to get boring, you need someone he can talk to, discuss things, argue about which direction to go, have to save or be saved by, it doesn't have to be a love intrest, it could be a friend or some random person who happens to be travelling in the same direction.

And things that could happen on the road: he could get ill, he could run out of supplies, etc. And what's the path like? does he have to swim across a dangerous river because the bridge is broken, climb a mountain because it's the quickest way to where he's going? Isn't there someone trying to stop him from finding his sister?

So yeah, that's my opinion and my suggestions there. I hope they help and don't cause offence or anything because none was meant.

If I get you right the sisters motive is the quest but the brothers doesn't know. So his motive is only, to get her back?
Than you should strengthen this motive. Maybe:
- When she fled home, she took an item with her, he desperately needs to get back,
- She has an ability he needs (to heal his mum),
- He is accused of wrongdoing but she knows better and he needs to bring her back as a witness

This sounds like a lot of what I was doing in my current WIP--characters who needed to have SOMETHING happen to them, and so I was looking for little mini plots to fill out their stories. I brought in rescues, encounters with rogue Saxons, wannabe magicians, bear attacks, and so on.

Now I'm working on my 2nd draft of the novel and guess what I have to do? Cut ALL those little subplots out. (Well okay, I'm keeping a handful of them.) They made the story too fragmented and rambling; they were just wandering about in these little miniature plots that finished and never made any difference to the story afterward, and it made it feel like I had nowhere to go.

This may not be what you want to hear, but my suggestion is to consider untying your book from the sister chapter, brother chapter format and skipping the parts where you would otherwise insert filler stories. There is no law that says that with multiple POVs you have to strictly alternate between them. I wouldn't see any problem with having a brother chapter every three or four chapters instead of every other one, especially if the sister has the more important story at this part of the book. As long as it's clear whose POV each chapter is from (quite easily accomplished by making sure to drop his/her name in the first few sentences) this would work out great.

If you do decide to stick with the alternating chapters, my best advice is to find one lengthy subplot instead of many smaller events. Of the filler chapters I came up with for my WIP, the one that actually became something useful--something where a character underwent a real change--was the storyline that spanned several chapters. A longer storyline will get the reader involved and wanting to know what's next in a way that separate smaller events can't.