Day One
Battle Level: 01 Recommended Stats: lv1
Start by walking up to Roxas' crew, and after that walk up to the lady at the accessory shop. Lock on (L1) to the cat, and some cutscenes will ensue.
You are presented with three weapons -- each of which you can use the appropriate Reaction Command (Triangle, hereafter referred to as RC) to select, and each of which gives Roxas a stat boost, as follows (right to left):
Bat Used for the Struggle Battles: +1 Attack. Guard Bat (lit. stick with hand guard): +1 Defense. Staff: +1 Magic.
Seifer
For the first encounter, all you have to do is a basic combo with finisher.
For the second battle, whack at him until he's dead (about thirteen hits). Lock on to keep track of his movements. Sometimes, he'll do a double-strike attack, so keep your distance occasionally.
After that, follow the Nobody to The Old Mansion, and perform the RC on the Nobody. A small cutscene ensues.
Dusk
Go ahead and try to attack the Dusk -- it's not going to work. You can also get the feel for RCing in battle with the Slide Turn.
Eventually, a cutscene will show, and Roxas will gain possession of the Kingdom Key. Use this to finish off the Dusk, and remember to Slide Turn to avoid the Dusk's attacks. It takes eight hits to finish the Dusk off.
You'll lose the Keyblade in the next cutscene, unfortunately. On to day two, but not after a bunch of cutscenes and another flashback.
Day Two
The Usual Spot
You'll start off in The Usual Spot -- take note that you can finally save. Go over to it and RC to save. Players stingy with their data usage should take note that a typical KHII save takes 87KB, which is small enough to merit a save per world on a blank/dedicated KH2 memory card in case you want to revisit any story aspects.
Back Alley
A cutscene will place you in the Back Alley, where you can RC to use the skateboard to the right of you. Take the path to your left.
Plaza
Check the boards for some part-time jobs to earn munny with, as follows:
Letter Delivery
This mini-game serves as training in RCs. As you pass by people (and random birds) on your skateboard, RC to deliver them a letter.
Luggage Transfer
Attack the cart (uphill, that is) into the garage. When the cart gets into the air, smack it more to proceed even further.
Performance at the Station Heights
Juggle the ball with your non-Keyblade-y weapon of choice, with whatever combos you can throw at it. The game will keep track of your high score.
Poster Pasting
Find spots on the walls to paste posters using RCs.
Bee Extermination
Kill the bees with your weapon of choice. Remember to lock on, of course.
Junk Cleaning
Attack the junk to clear it from the field. You can also hit junk into each other for a more effective cleaning.
You need only do the first three tasks, but the game gives AP bonuses for acquiring enough munny -- 2 AP for approximately 1200 munny. You'll know you've reached it when the game takes you to the next cutscene automatically. However, if you just want to play, then talk to Heine in the Station Plaza.
You'll acquire the Munny Pouch for your efforts.
Day Three
Meet your friends. After some odd cutscenes, prepare to defend yourself...
Dusk
You'll encounter a Dusk again, but without the Keyblade. Just employ the tactics as in the first fight, and another cutscene will displace you from Twilight Town.
Does the following scene look familiar?
Dive into the Heart
Station of Serenity
Remember the tutorials from the first Kingdom Hearts that told you to choose a strength and a weakness? Well, they're baaaaaack. RC to select between the sword, shield, and wand, which stand for Attack, Defense, and Magic respectively. If you press Select to switch to First-Person Mode and look around, you can see the Dusks just waiting there.
When you acquire the Keyblade, they attack.
Dusk Team
Same as before...except now there's three. There's nothing to worry about, however -- just Slide Turn like hell. You'll get the Air Recover ability for your efforts.
A familiar door appears, along with another save point. Take the time to equip your items and equip abilities if you haven't done so already (Start button).
Station of Calling
Go up the stairs. Fight Dusks. Go up some more stairs to the door. This is a good opportunity to get Roxas ready for the battle ahead.
And then, when you open the door, one helluva big Nobody comes out of nowhere. Roxas' actions (and the way the camera moves) should look familiar to veterans of Kingdom Hearts. ;)
Twilight Thorn battle
The fight will start with you paralyzed in the air. Perform RCs at the appropriate times to counter and cause damage to it. The Nobody will disappear into the darkness, only to topple the platform and do another cool-looking RC-counterable attack.
Then the main phase of its attacks starts. Avoid the white thunder attacks by RCing and by Slide Turning, hitting its head whenever you can. Eventually, the fight will repeat itself, resulting (hopefully) in you winning the fight. Use a Potion if you have to.
Bonuses
HP Up, Reflect Guard ability