The antonyms for the phrase "toughening up" can be a little subjective, but some possible options include "softening," "sensitizing," "vulnerabilizing," "gentling," and "weakening." Each of these words implies a different approach to personal growth and resilience, with "softening" and "gentling" suggesting a more gentle and compassionate approach, while "sensitizing" and "vulnerabilizing" highlight the importance of emotional openness and empathy. "Weakening," meanwhile, suggests a more negative outcome, in which someone becomes less resilient and adaptable. Ultimately, the antonyms for "toughening up" suggest a range of ways to develop emotional intelligence and navigate life's challenges with strength and flexibility.