Antonyms of callous :
sensitive, tender, untoughened, benevolent, benignant, gentle, kind, clement, indulgent, lenient, mild, cordial, friendly, good-natured, good-tempered, gracious, tolerant, understanding, affectionate, fond, loving, charitable, compassionate, humane, kindhearted, kindly, merciful, softhearted, sympathetic, tenderhearted, warm, warmhearted.
Examples of usage:
Now it was because of the operations which he dignified by the name of wars, and now because he had no ship suitable for sending to Jamaica; but the truth was that Ovando, the springs of whose humanity had been entirely dried up during his disastrous reign in Espanola, did not want Columbus to see with his own eyes the terrible state of the island, and was callous enough to leave him either to perish or to find his own way back to the world. "Christopher Columbus, Volume 7 And The New World Of His Discovery, A Narrative", Filson Young.
And for long the Kaiser kept that callous, imperious look. "Tales of War", Lord Dunsany.
But when I think of her callous reception of the tidings of the unhappy boy's death, my spirit fails me. "The Morals of Marcus Ordeyne", William J. Locke.