Rashnu is not a topic that a five-year-old would understand, as it is a Zoroastrian concept related to the afterlife and judgment of the deceased. However, I can try to explain it in simple terms.
In the Zoroastrian religion, when a person dies, their soul travels to a place called the Chinvat Bridge, where it is judged by Rashnu, one of the yazatas or divine beings.
Rashnu evaluates the person's deeds during life and determines whether they were good or bad. This judgment is based on the concept of ethical dualism, which means that actions are either good or evil, and there is no gray area.
If the person's actions were good, they are allowed to cross the bridge and enter the paradise called the House of Song. However, if their actions were bad, they are thrown off the bridge and fall into the underworld, where they suffer eternal punishment.
In summary, Rashnu is a divine being who judges whether the souls of the deceased will enter paradise or suffer punishment in the afterlife.