Crucial, adjective: Pivotal, critical, key, climacteric, decisive, deciding; life-and-death; all-important, of the utmost importance, of the essence, critical, preeminent, paramount, essential, vital.
Malignant, adjective: Virulent, very infectious, invasive, uncontrollable, dangerous, deadly, fatal, incurable, life-threatening; cancerous; technical metastatic; spiteful, malicious, malevolent, evil-intentioned, vindictive, vengeful, malign, mean, nasty, hurtful, mischievous, wounding, cruel, unkind; informal bitchy, catty; literary malefic, maleficent.
Yearning, noun: Longing, craving, desire, want, wish, hankering, urge, hunger, thirst, appetite, lust, ache.
This yearning was malignat
Thoughts that were cruicial
Changing the person inside