You wake up with amnesia, and have to figure things out by shooting lots of people...

After you shoot enough people, one guy yells out what happened. He tells you that the King Acid Bird attacked you. He tells you that if you want to defeat him, you must awaken the 7 Guardian Acid Spirits. He has 6 left since the man you talked to is one of them. They are located in the Forest, Volcano, Oceans, Dessert, Cemetery, and one is in disguise. You start to walk to the forest, when suddenly...

You need to put a game breaking bug that happens in certain conditions and the only know fix is to restart form the previous level to avoid the corrupted checkpoint. And the game dev must have a 200 page forum thread about it and still no patch released.

I forgot to mention, there's a game-breaking bug right before my previous post. You can shoot the Guardian Acid Spirit before the cutscene!

You meet a small girl with strange powers and a dark secret, you have to take her around with you because she is your only link back to the human world where you were an accountant, which of course you keep having flashbacks to. The little girl constantly complains as you set out on your quest with her power to get inside your head so you must placate her by acting out tales from your accounting days. She realises with you accounting skills you can defeat your enemy so you become an expert, after getting amnesia a few more times and repeating all this you convice the King Acid Bird to sign a peace treaty but... 

...The Zombie Apocalypse starts! You lock and load, and you're ready to go! Suddenly, the King Acid Bird gets infected and...

you remember your chainsaw, blessed by ancient priests with zombie killing power. You team up with a rag tag team, a nerdy scienist, an older commanding gentleman of some kind and a tough as nails woman to find the ultimate chainsaw but you never do, instead fighting the zombies with their averation for loud jazz music which you must play whenever around them, all hope seems lost when...

an italian plumber trying to save a princess that was kidnapped by an evil turtle monster!

The Guardian Acid Spirits appear from nowhere and stop the zombies! But, the Acid Birds come and...

They spit out juice that turns everyone including your friends into Giant Acid Birds. A Microsoft Sam voice says "Oh no, everyone has turned into Giant Acid Birds and they will exterminate you like a Dalek now. Wow."