Lechna was an alleged lover of Aeryn Sun.
When Captain Jenek asked Vreena, the Sebacean nurse, if she has matched Aeryn Sun's embryo's DNA, Vreena reveals that it is a pattern which has not been cataloged in their memory banks. Vreena indicates to Jenek that it could be half-human. Because they have no sample of Crichton's DNA, the two interrogate Aeryn Sun, trying to get her to tell them if the father of her fetus is Crichton. Aeryn tries to hide Crichton's name by telling them about someone called Lechna. Aeryn says that while she was away from Moya, she was an assassin, and this Lechna was both her contact and also her lover. Aeryn further elaborates, saying she tried to suppress this fact until now to protect him, and her fetus is most likely his conception. Lechna, she says, is from a place called Vendrall, a small planet off most charts.
It sounds plausible, and Jenek has heard of it. It is, he says, in the Callus Nebula. Shortly afterwards Vreena crosschecks the DNA with other samples from that area, and finds that it doesn't match. Aeryn lied.
Lechna may or may not exist, and he may or may not have had a part in Aeryn's time apart from Moya. In the episode "Promises", her return to Moya, desperately ill and under the care and protection of Scorpius, seemed to indicate that she left some sort of group of subversives under dire circumstances, having apparently completed at least one assassination. This Lechna may have been a member of this group or another character from Sun's past.
Reference: Transcript here.
- (4.18 "Prayer") (mentioned)