Are there any asura that asked for a boon/wish and they didn't became evil?

Question

There are many asura's that asked for wishes and became evil. Example ravan.

So are there asura's that were good even after there wish were full filled. Any examples of those asura who's boon itself was about power and strength.

Answer 1

Karkati is one such example. She takes boon from Brahma and realizes later to become good and becomes Jivan muktha.

Her story is mentioned in Part 3 - The Story of Karkaṭī in Utpatti-prakaraṇa of Yoga-Vasistha

Initially, she performs an intensive tapas and asks Brahma for a boon as follows

After she had passed thus a painful Tapas for 1,000 years, the Lotus-seated Brahmā appeared visibly before her. Are there any objects which cannot be acquired in this world even by the vicious through the performance of rare Tapas? With the arrival of Brahmā before her, she made obeisance to him mentally without stir ring from her spot and reflected thus: “In order to assuage my ever-increasing fire, if I transform myself into the form of an iron-like Jīva-Sūcikā (living needle). I can enter into the bodies of all in the world and consume as much food as I require.” Whilst these thoughts were revolving in her mind, Brahmā asked her the object of her wish. Karkaṭī replied thus “Oh Lord that favorest those, thy devotees who contemplate upon and praise thee. thy servant wishes to be come a Jīva-Sūcikā.”

After obtaining boon from Brahma, she utilizes her boon and harms others. But, afterwards, she realizes about evil in her and performs tapas again for Brahma with pure mind and finally gets liberation.

So saying Brahmā vanished from view, whereupon this mountain-sized personage reduced herself to the size of a Jīva-Sūcikā and entered into the minds of the ferocious as well as the timid in order to make them perish. Having entered in the form of Vāyu within all Jīvas in earth and in Ākāśa, she fed upon all their lives in the form of Jīva Sūcikā and Vāyu-Sūcikā. Surfeited with such an enjoyment, she exclaimed “Whirling and making me despondent, my desires do make even the needle to wear away and making me giddy, do destroy me. Away with these desires of mine ! With a cruel heart. I have afflicted many lives in vain. Therefore, I shall divest myself of all desires and perform Tapas in the Himalayas “So saying, she gave up all fluctuation of mind, devoid of any longing- for objects. Thus a thousand years passed, purifying her of the two-fold Karmas, (virtuous and sinful). While thus, she was engaged in spiritual contemplation with an illuminated mind, free from all the pains of love and hatred and slighting this universe, the all-full Jñāna dawned in her mind and therefore Brahmā came voluntarily to her and imparted to her the following truths: (< Thou hast attained the Jīvanmukti state. Thy mind has been quite illumined; yet thou shalt be in thy old form of a Rākṣasa lady and sup port thyself on earth in the bodies of persons without Jñāna as well as the cruel and the base. Happiness thou shalt en joy thus.” With these blessings, Brahmā disappeared.

Answer 2

Vibhishana is an example. He asked for a boon that he should always be righteous and also obtain the light of divine knowledge from Brahma

http://www.sacred-texts.com/hin/m03/m03273.htm

Brahma then addressed Vibhishana, 'O my son, I am much pleased with thee! Ask any boon thou pleasest!' Thereupon, Vibhishana replied, 'Even in great danger, may I never swerve from the path of righteousness, and though ignorant, may I, O adorable Sire, be illumined with the light of divine knowledge!'

Brahma was so pleased by him that he even bestowed upon him immortality.

And Brahma replied, 'O scourge of thy enemies, as thy soul inclines not to unrighteousness although born in the Rakshasa race, I grant thee immortality!'