Lord Krishna was an Avatar, which means a special highly evolved soul, which descended on this Earth to accomplish tasks related to reestablishment of human values and to curb the negative forces. In case of an Avatar the time selection becomes more important due to importance of various tasks.
Krishna was born with both his ascendant and the natal Moon falling in the Rohini Nakshatra. The main deity of Rohini Nakshatra is Lord Brahma the creator. So for all affairs of this Earth this nakshatra becomes most important. In order for Krishna to take help of the Mayavik (delusive) force on Earth in order to accomplish many difficult tasks his birth in this Nakshatra was necessary.
This Nakshatra gave Lord Krishna a special charisma for mesmerizing those who would not listen to him otherwise.
Rohini Nakshatra gave focus and great perseverance in order to accomplish difficult tasks such as killing the ruler Kansa and many other demons.
Lord Krishna was born in Rohini nakshatra.
It was due to Rohini nakshatra that Lord Krishna’s life was a presentation of esoteric romance in order to lure the wayward human souls back to the divine realms. Planet Moon and Venus connected with the star were responsible for Lord Krishna’s extremely attractive and sweet personality with polite mannerism. Rohini Nakshatra is a Rajsik Nakshatra so it gave lord Krishna an action oriented personality, yet due to his divine origin he remained pure as a lotus in a pond of dirty water.