The Toy Store Mechanic: Secret War Machines

While chasing a fugitive, the police stormed a small toy shop, only to find something ten thousand times more dangerous: a fully functional heavy combat mech. The scientific world was sent into a frenzy as world-class professors fainted at the sight. It turns out the "toys" he has been building in his garage are actually era-defining weapons. Now, the entire world wants to know: who is the mastermind behind the counter?