(covers information from several alternate timelines)
Esilia was an Ikaaran woman whose ship, in an alternate timeline in which the Enterprise NX-01 was thrown back in time from the year 2154 to 2037, was rescued from a field of spatial anomalies in the Delphic Expanse by Enterprise's captain, Jonathan Archer.
Esilia and Archer were eventually married and had children, a descendant of whom was Karyn Archer, who went on to become Enterprise's first officer. The timeline in which these events occurred was eventually negated when the Enterprise crew's descendants were able to intercept their counterparts and assist them in avoiding the accident which had thrown them back in time. (ENT: "E²")