In the animated version of Attack on Titan, Allen first transforms into a man in episode 7 of the first season.
In this episode, Alan and the rest of the Training Corps are stranded in the Troucester District, facing countless giants with little hope of survival.
In such a desperate situation, Eren transforms into a giant for the first time. His body changed drastically, becoming extremely hard and his muscles becoming unusually developed. His strength and speed have been greatly improved, allowing him to move freely through the huge crowd.
Allen's transformation gave him and the rest of the training corps a chance at life. He used his strength to defeat numerous giants and open a way for them to escape. However, this transformation process also cost him a lot of money. His body was badly damaged and had almost reached its limit. Over the next few episodes, Allen's body gradually recovers, and he gradually grasps the power of giants. He began to use his abilities more effectively to fight the giants. His transformation and strength also made him an important member of the training corps. However, as the story progresses, Alan gradually discovers his destiny and calling. He realizes that he is the only one who can stop this catastrophe and that he must use his power to save humanity. So, he embarked on a long journey to fight for the future of humanity. In the process, Alan has grown and changed. He encountered many difficulties and challenges, but he never gave up. His courage, perseverance, and determination gave him strength, as well as hope and courage to others. In the end, he succeeded in fulfilling his mission and winning for humanity. 