Unifier Qin is a new leader persona in the Rulers of China DLC as part of the Leader Pass.

Qin's special ability is all melee units (like warriors) get a Convert Barbarians action, that will pwn all adjacent barbs.

Mandatory:
Zombie Defence game mode.

Recommendations:

• Modes: Barbarian Clans, Dramatic Ages, Monopolies & Corps
  
• Speed: Marathon
  
• Map: Pangaea

Because barbarian behaviour is so unpredictable, a Qin game depends heavily on RNG.
The start is tricky and hard.

But once you get zombies to snowball, you can relax.

It is very important as Qin to locate a barb spawn early,
and to use your starting warrior (or another melee unit) to convert those barbs to your army.

The first thing you need for zombies to snowball is...a zombie!

Convert a zombie ASAP.

Use that zombie to kill weaker units.
This will spawn more zombies.
Use your first zombie to convert the spawned zombies.

(It is essential that every Convert Barbarians actions is considered: you need to convert at least one other zombie and/or melee unit when you use this action because your original unit is consumed when you do so).

See also guide How to Infinite Zombie Spawn. (Only Qin has no need of Zombie Defence special projects to levy zombies).

Once a governor title unlocks choose Moksha. His second promotion Laying of Hands heals all units in one turn.

Pick a city zombies spawn.
(Usually caps).

Assign Moksha to that city or cap.
Form a wall of zombies around your city and fortify.

As long as they have >1 health they will survive the turn thanks to Moksha.
And they will spawn zombies from kills next turn.

This will passively increase zombie Mutation Strength with every turn.

Let zombies do all the work!

With Unifier Qin's ability, his UI The Great Wall isn't of much real use for defence.
But it does generate gold.

Each zombie costs 1 GPT to maintain, so once you amass a zombie horde you may find yourself going bankrupt. So it is essential to build those walls to help maintain your army.

As Qin you may want to raid villages rather than disperse them in Barbarian Clans mode.

Focus on the flatland and hills clans as they will spawn melee barbs.
On most maps these are the most common anyway.

You can disperse others, especially seafaring and chariot clans.

Because zombies can spawn almost randomly out of nowhere, it is essential you garrison every city with a melee unit.

If zombies spawn, use it to convert them ASAP.

As zombies are your primary military force, your army is mostly disposable.
So sacrifice your obsolete units to zombies (to spawn more zombies).

Think of it as a trade up.

Boesthius:
PotatoMcWhiskey:
SpiffingBrit: