Our Xenoblade Chronicles guide features a comprehensive walkthrough and additional info on the endless amount of optional content in the game.
Walkthrough: Makna Path / Forest
Head down the path in front of you and a cutscene will ensue. You'll regain control of your team in a lush forest. There are a slew of new enemies here, hovering around level 28. This is the first time in the game that common enemies present a formidable challenge, especially in groups.
When you reach the Agni Tablet landmark, there's a group of Nopons that provide opportunities to shop or pick up quests. It would be a good idea to descend the cliff nearby in order to reach the Lakeside Landmark. There is a Water Ether reserve there that will come into play very soon. Reaching the landmark now will allow you to warp there, rather than backtrack.
Crossing Bridge 1 is your next step. Continue northeast towards the goal and your team will discover an incapacitated girl. The team needs a potent ether source to revive her. Shulk will venture out on his own, but rather then walking all the way back, just open your map and skip to the Lakeside landmark. Nab the crystal when you get there to complete the "Mystery Girl Rescue" story quest.
You'll also meet a curious fellow, and quickly get thrust into battle with three Puera Telethia. It's not a difficult fight and it serves to introduce two new aspects to the battle system.
Aura / Purge Art
From here on out, certain enemies (usually Telethia), will posses an aura. Auras can bolster their defenses, grant status boosts, and induce the ability to inflict Spike Damage (more on that below). Using Shulk's monado Art, Purge, will seal the aura temporarily, reducing the enemy's advantage in battle.
There's nothing good about spike damage, that's for sure. Many enemies posses the ability to inflict Spike Damage and it's impact is not effected by status protection or defense capabilities. You'll receive damage from some enemies by attacking them (the spike is a counter attack), attacking them when toppled, or even by simply getting too close.
Reyn will show up after the battle and take you back to the mysterious girl. Once she's revived, you'll learn a little bit about who she really is.
Melia's her name, and she's going to lead your team to the Nopon stronghold known as Frontier Village. Follow the marker at the top of the screen and you'll have no problem finding the entrance. As you approach, there's a few titans roaming the ground beneath the footbridges. No worries, luckily they have no interest in your team.
There is an apparent mistake in Special Lever 2 for Regbuilding Colony 6. It says defeat Earth Nebula at Sap Cave. I was never able to find a Sap Cave, but I was able to defeat Caris Nebula at the brog lake just before you get to Nopon Arch.