Virulhaka is the Heavenly King of the south and one who causes good growth of one's inner character. He is the ruler of the wind. His symbolic weapon is the sword which he carries in his right hand to protect the Dharma and the southern continent. Also, the sword represents wisdom: if you have wisdom, you will not be troubled by worries and problems. Wisdom sword helps us to cut off stupidity and ignorance. Therefore, Virulhaka's sword symbolizes that one should strive hard to improve one's knowledge and morality each day.
In Buddhism, the Four Heavenly Kings are four gods, each of whom watches over one cardinal direction of the world.
The Four Heavenly Kings are said to currently live in the Caturmaharajika Heaven (Four Great Kings Heaven/四天王天) on the lower slopes of Mount Sumeru(須彌山), which is the lowest of the six worlds of the devas of the Kamadhatu (Realm of Desire/六欲天). The four Heavenly Kings are located at the north, south, east, and west sides of Mount Sumeru because they are the protectors of the four continents of our world: Purvavideha to the east(東勝神洲), Jambudvipa to the south(南瞻部洲), Aparagodaniya to the west(西牛賀洲), and Uttarakuru to the north(北俱蘆洲). They are also the protectors of the world and fighters of evil, and each can command a legion of supernatural creatures to protect the Dharma. They have a five-hundred-year lifespan, of which each day is equivalent to 50 years in our world; thus their total lifespan amounts to about nine million years in human calendar. All four serve Sakra(the Lord of the Devas/帝釋天) of Trayastrimsa(忉利天). On the 8th, 14th and 15th days of each lunar month, the Four Heavenly Kings either send out messengers or go themselves to see how virtue and morality are faring in the world of men. Then they report upon the state of affairs to the assembly of the Trayastrimsa devas.
They are vowed to protect the Buddha, the Dharma, and the Buddha's followers from danger.