In Dragon Quest IX: Sentinels of the Starry Skies
, you are a Celestian, an angel. Your character is the "Guardian of Angel Falls." While watching over your village, you and your mentor have to protect two people from monsters. The humans give thanks to you for protecting them on their journey, even though they don't see you. This thanks turns into Benevolessence, which you have to then take to the Great World Tree, Yggdrasil. After you do this and get back to your village, you'll wander around town helping the townspeople for a bit. As soon as you have a few more crystals, you go back and take them to the tree. Finally, after thousands of years, the tree blooms and the Celestians think that they are going to be allowed to finally return to the great being. Just as the Starflight Express train lands, it explodes and everything is torn to bits. You wake up back on Earth as a human!
First thing that you're going to have to do is help the town get connected to the world once again since a landslide blocked the only road in and out of it. But the mayor's son asks you to help him do this, so you're not going to have to go at it alone, at least. Ivor's a bit of a brat, but at least he's a decent fighter. On your way to the landslide, you come across the Engine Car to the Starflight Express. Ivor can't see it though! You'll soon meet someone who can help you get going on that train again, but first you're going to have to collect enough Benevolessence that you get your celestial powers back again. Eventually, you'll make it back to the observatory and your real quest will begin. You have to go back to Earth and collect all the Fyggs that fell from Yggdrasil when it bloomed. They're a danger to the mortal world. From here on out, the game basically involves you traveling to very remote areas in search of these Fyggs. Luckily, you can always warp back to any previous location, which is very important to the quests.
In addition to the main storyline, there are a lot of quests for you to accomplish. Talking to certain people triggers quests for them. They'll tell you what you need. Some of them can be accomplished right away and some will take some time to find those items. There are also recipes that you can use to make things, a whole lot of recipes. If you want to collect them all, you'll have a lot of work to do!
Just in case you happen to want to quest with your friends, you can also play with a total of 4 people wirelessly as long as they have their own copy of the game. It'll give you quite a few additional things that you can't get from just playing alone!