Eingyi blocks the entrance to Quelaag's Sister. He will ask the player if they are there to serve his master; the player must answer yes to access Quelaag's Sister, and thus, the Chaos Servantcovenant without killing him.
Eingyi was originally a pyromancer from the Great Swamp and was cast out due to the perverse nature of his Pyromancies. He later became afflicted with the unknown blight that plagued the followers of the Chaos Witches. Because of this, Quelaag's Sister felt pity and sucked out the blight pus from them. This action caused her to become gravely ill, strengthening the loyalty and adoration of her adherents.
Although Eingyi is devoted to Quelaag's Sister, he cannot speak her language; everything he knows about her and her past is through observation and extrapolation.
In terms of combat, Eingyi is identical to the other egg-bearers: he will feebly swing with his arms, attack with a Vile Maggot from his eggs, and, upon death, unleash a handful of the same maggots from his eggs to attack the player. Eingyi also has a chance of infecting the player.
...Oh dear...What have we here? Are you a new servant?
(...Hmph. But you have no eggs?*) Bah, no matter. Go along and have audience with Our Fair Lady. I pray that you will mind your manners!
Then you shall not pass. Away with you!
Speaking after Answering "No"
The nerve of you! Be gone, be gone at once!
Are you in need already? Well anything for the Fair Lady...What do you want?
Are you prepared to dedicate yourself to Our Fair Lady? Then I will make available whatever you require. If you need something, ask me first.
Talk x1 Before being infected with eggs
...There is nothing to say to you...Except...If you lay a hand on the Fair Lady, you should be prepared to face my wrath.
Talk x2 Before being infected with eggs
There is no time for idle chat. Think only of Our Fair Lady, and what she may need.
Greetings after understanding the Fair Lady's words
...You, you speak the tongue of the Fair Lady? ... Well, do not be rash with your pride. You have yet to earn my trust. If you try anything funny with the Fair Lady, there will be hell to pay.
Speaking after being infected with eggs
Well! ...Now...you're just like me... Your dedication is fully apparent. Only well...Your head looks awful...Why not try this? I've no use for it any longer.
Greeting after being infected
Oh, hello. What is it that you need?
Oh, hello... A pleasure to see you again. But do not neglect the Fair Lady. She needs some company.
Talk x3 after being infected
Incidentally, do you have an interest in pyromancy? If you have, I shall share my flame with you.
You have served our Fair Lady well. Now, let this strength be yours.
...Well, fine. I will not force you.
Talk x4 after being infected and understanding the Fair Lady
In all honesty, I am envious. What comfort can I offer, without speaking her tongue?
Talk x5 after being infected
Worse than Undead, we are diseased, and unwanted. Like the grime of the Great Swamp. But my dear, Fair Lady! She cried for me... And swallowed the great Blightpus, despite Mistress Quelaag's orders to the contrary.
Talk x6 after being infected
Below us lies the ruins of the legendary city of Izalith. There, the Molten Giant watches over the Flame of Chaos. Our Fair Lady, and Mistress Quelaag, fled from the ruins. I do not know the details...And I do not ask...
Talk x7 after being infected
Have you heard of Lost Quelana? An inhuman witch, who wanders the Poison Swamp. Only no one has ever seen her, so who really knows? But what if she really is another one of the Quelaag sisters? Our Fair Lady would be greatly comforted by her presence.
I knew it! I knew it! You will not get away with this!
Hrg...rgggkt...My dear Fair Lady...You are in danger...
Killing Quelaag's Sister
Why, youuuuu monster…! The Fair lady! What have you done, what have you done! Hrggreeeeeeeeeeh!