221 BC was the year that marked the end of the Warring States Period in China.
Ying Cheng, the ruler of the Qin kingdom, established a totalitarian state in
his country, and soon began to invade other kingdoms, which resulted in the
unification of China and the establishment of the Qin Empire. Ying Cheng
became Qin Shihuang, the First Emperor. He mercilessly repressed rebellions
and forbade all teachings except those who praised him and his regime. At this
terrible time, Shuijing, a young girl who studied the secret science of the
Mohists (followers of the great Chinese philosopher Mozi), saw how the
teaching she followed became more and more deformed, departing from its
original rules. From the point she realized that she broke two important rules
of the Mohist school, Shuijing decided to dedicate her life to two purposes:
reform the teaching of Mozi, and defeat the Qin Empire.

Xuanyuan Jian 4: Hei Long Wu xi Yun Fei Yang is the first 3D installment of
the Xuanyuan Jian series. Both navigation and battles are fully 3D, and it
is possible to rotate the camera 180 degrees during exploration. The game
abandons the active time battle system of the third game, returning instead
to full turn-based system of earlier games. There is a wide variety of
techniques to learn, including the traditional magical spells and special
attacks that require stamina. The game introduces a special bar that appears
during battles, displaying the order of the participants’ turns. By attacking
an enemy who is about to act, it is possible to “push” it down the bar,
delaying its actions.

Like in the previous installments of the series, it is possible to capture
monsters and then summon them during battles. However, Xuanyuan Jian 4
expands this gameplay element to the “Heavenly Book” system, which allows the
player to build living quarters, weapon factories, shops, and temples,
populating them with monsters. Each monster contributes unique parameters to
the building he is in. By collecting various raw materials (wood, gold, etc.)
and balancing the required parameters for the facilities, the player can
create his or her own weapons, armor, accessories, and items, learn new
spells, and enhance the abilities of summoned monsters.