(Idea) Final Fantasy: Undead Crisis

This is an idea I had while playing SAS 4 and just a mention atm I don't have PC to work on my projects.

I was thinking of how the mechanics in the Kefka battle worked on the Narshe mountain where you switch party members and the enemies have a "goal" the idea is to set Zombies to chase the player through a large city based map while the player completes the story. 

Story base (Also an idea of the top of my head)

Enter New Midgar ruins
As a young MP Cloud strives to survive in this crisis after being given a mission to survey and eliminate the target. During the arrival the team is attacked and most members are killed, a handful are scattered and even infected.

During the story the player must interact with people and objects to continue and further the story also while setting up defenses to help block out the onslaught. You'll find the past events in story set safe rooms in notes about the project that Hollander, Hojo, Shinra, and Dr. Kollar and his team (That are still in the city)have created.

The notes will be logs kept during the events as they progressed up to the outbreak. The project stims from the belief of creating an Undead army using the life stream and Jenova cells and some other methods on the dead. But the scientists didn't realize where it would lead.

Story & Mechanics-
The game will be more survival than difficulty so you have to be prepared. There's safe rooms, and the apocalyptic merchant "Scotty Boy" Who sells all sorts of items and tells his "fun" experiences during the crises. Forever holding his sense of humor.

Later in the game the player can buy other characters to play as (As a fun feature) that have setups that make the game funner or easier)
Such as:
Cloud (Soldier)
Cloud (Advent)
Zack
Angeal
Sephiroth
Dante (Devil May Cry)
Nero
Goku 
Vegeta
Prinny (Disgaea)
Dragonborn
Chris Redfield
Jill Valentine
Randy Savage (Obvious reasoning)

Weapon Mechanics:
Guns consume MP along with tactical skills like "Molotov or Grenade" You replenish with "Ammo Box" sold buy Scotty Boy or as enemy drops.

Swords:
High damage and front row use. Due to the game breaking "No ammo" requirement it'll be on sword based characters only. While sum can still use low damaging weapons like "Police Baton" 

Items (to name even more ideas)
Medkit :Health

Jenova stim pack: Full health and status recovery

Ammo Box/Crate: Ammo (MP) recovery.

Flak Jacket: Raises defense 

Shinra Training Manual: Raises damage

Spare Clips: Raises total amount of Ammo

Etc. 

Talk to me and we'll see if it's worth making.

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I also forgot to mention that I can help writing stories.