Here is the story of Arjunmali as told in a popular Jain tradition:

Arjun was a gardener in Rajgriha. He was kind, devoted, and used to worship a Yaksha near his garden. One day, while his wife Skandashri was going to the temple with flowers, six lustful men saw her, dragged her into the temple, and violated her. When Arjun came there, they tied him up as well and continued their cruelty in front of him. Arjun felt deep humiliation and pain. In some retellings, this shock became the turning point through which a Yaksha entered his body, after which Arjun transformed into the fierce being known as Arjunmali. ( jainsite.com)

After that, Arjunmali became extremely violent and began killing six men and one woman every day. Because of this terror, the people of the city stayed inside and no one dared to go out. When Lord Mahavir came near the city, the citizens were too afraid to come out and receive him. ( jainsite.com)

At that time, Sudarshan went forward with great devotion to see Lord Mahavir. Arjunmali rushed toward him, but Sudarshan stood firm in kayotsarga and took refuge in the Navkar Mantra and in the Lord. Because of the power of truth, devotion, and inner steadiness, Arjunmali could not harm him. In one version, the Yaksha then left Arjunmali’s body. Arjunmali was stunned, asked what had happened, and Sudarshan explained everything to him. Hearing this, Arjunmali repented deeply. ( jainsite.com)

Then Arjunmali went with Sudarshan to Lord Mahavir. There, he listened to the Lord’s discourse, renounced worldly life, and later endured the anger and beating of the relatives of those he had killed with patience. Through this deep repentance and forbearance, he attained kevaljñān and ultimately moksha. Sudarshan also renounced the world and attained liberation. ( jainfoundation.in)

The main lesson of the story is that even a person who has committed terrible violence can change through sincere repentance, right faith, self-control, and patience. It also shows the Jain power of Navkar Mantra, truth, and forbearance. ( jainfoundation.in)

If you want, I can also give:

• the story in simple Hindi
• the story as a short children’s version
• the moral points from the Arjunmali कथा