Does the sexual relationship that occurred between the paternal aunt and her brother's son—against her will and while she was in a psychological state, with him exploiting her condition—count as zina (unlawful sexual intercourse), and what is the path to repentance and rectifying this act?

Incest is one of the most heinous crimes and an indication of a perversion of fitra (innate disposition). Its sinfulness is not lessened by enticement or psychological illness, unless it leads to a loss of perception and free will. One must hasten to sincere repentance, fulfilling its conditions: abandoning the sin, feeling remorse, resolving never to return to it, staying away from causes of temptation, increasing good deeds, and strengthening one’s connection with Allah. This should be done while concealing one's sin and not mentioning it to anyone, for indeed, repentance erases what came before it.