Kamika is a Hindi and other India regional languages feminine word-name, used across India. Kamika means desired. Ekadashi means the 11th lunar day. The number 11 in Sanskrit is called Ekaadasha. Any Ekadashi happens twice a month, one in each of the two lunar phases. The two lunar phases are the Shukla Paksha and the Krishna Paksha, i.e., waxing-rising moon phase, waning-descending moon phase, respectively. The Ekadashi dates are best reflected in the Hindu lunar calendar. Kamika Ekadashi falls in the Hindu calendar month of Shravana (in parts of July-August) in the Krishna Paksha, as per Gregorian calendar, it falls on the 7th of August 2018.
Kamika Ekadashi is observed in remembrance and devotion to Lord Vishnu. Many devotees observe Vrat, fasting. Devotees seek Lord Vishnu’s blessings. Devotees seek forgiveness for any sins. They ask for a solution to any problems. Devotees pray for the completion of their desires. They offer Tulsi leaves to Lord Vishnu. They light ghee or sesame filled oil lamps, Diyas. Worshiping Lord Vishnu on Kamika Ekadashi is believed to relieve natives of the Pitra Dosh, also Pitri Dosh, death rites, and to pay homage to the ancestors.
Story outline and as per ancient texts behind Kamika Ekadashi is that once there was a demon named Murdanav. The demon once challenged Lord Vishnu to fight. However, Lord Vishnu was in the state of a long waking-sleeping state, called Yoga Nidra, at this time. Then a female appeared from his 11th sense, Ekaadasha. Demon Murdanav was attracted to this female and wanted to marry her. To this, she put a condition to him to fight her first. The demon was killed by her in the fight. Therefore, being happy, Lord Vishnu granted that her to be named after the Ekadashi. She wanted Lord Vishnu to forgive people who observed Vrat on this day. That is also why devotees observe the fasting on Kamika Ekadashi.
A common Mantra for Lord Vishnu is—
Om Namo Bhagavate Vasudevaya
ॐ नमो भगवते वासुदेवाय