Domon Kasshu is the main protagonist of Mobile Fighter G Gundam.

Domon was seen as brash, impulsive, emotional, and extremely impatient. Domon was very prone to letting his emotions overcome his better judgement, but that was usually leveled off by his partner, Rain's even-keeled personality. Domon was also highly determined to free his father from his frozen imprisonment and find out why Kyoji had stolen the Devil Gundam. Despite the obsession that Domon demonstrated about his mission, he possessed a strong sense of justice, and would usually set aside his own mission when the weak and powerless required his protection.

Although he has been lonely in spite of his family since childhood, and his clumsy roots have caused him to avoid contact with others more than necessary, he is in fact a good young man with an honest and kind nature. Because of this, his mentor, Master Asia, has called him "a fool who loses sight of what is necessary at the most important time" and "a fool who is slow to make decisions." Through the tragedy of losing his friends, his beloved brother, and his mentor, he overcomes his weakness and grows up a lot.