There is perhaps no other scene from Irish mythology that causes more confusion than the imcallam na Morrigna or so-called 'Buan's Daughter' section of the Táin Bó Cuailgne [TBC]. This is the scene where the Morrigan in disguise as the daughter of a king named Buan [literally 'lasting' or 'enduring'] goes to Cu Chulainn and first tries to tempt him then threatens him.
This is the Faraday translation of the passage:
"Cuchulainn saw a young woman coming towards him, with a dress of every colour on, and her form very excellent.
' Who are you? ' said Cuchulainn.
'Daughter of Buan the king,' said she. 'I have come to you; I have loved you for your reputation, and I have brought my treasures and my cattle with me.'
'The time at which you have come to us is not good. For our condition is evil, through hunger. It is not easy to me to meet a woman, while I am in this strife.'
'I will be a help to you..
[edited out from Faraday the original text is Cu Chulainn's response "It is not for a woman's arse I have come."]
.. I shall be more troublesome to you,' said she, 'when I come against you when you are in combat against the men. I will come in the form of an eel about your feet in the ford, so that you shall fall.'
'I think that likelier than the daughter of a king. I will take you,' said he, 'between my toes, till your ribs are broken, and you will be in this condition till a doom of blessing comes (?) on you.'
'I will drive the cattle on the ford to you, in the form of a grey she-wolf.'
'I will throw a stone at you from my sling, so that it shall break your eye in your head; and you will be in that state till a doom of blessing comes on you.'
' I will come to you in the form of a hornless red heifer before the cattle. They will rush on you on the plains (?), and on the fords, and on the pools, and you will not see me before you.'
' I will throw a stone at you,' said he, 'so that your leg shall break under you, and you will be in this state till a doom of blessing comes on you.'
Therewith she goes from him."
The text following the edited portion is nearly a duplicate of the final back and forth between the Morrigan and Cu Chulainn in the TBR where she threatens to come at him in the three forms to make his combat with an equally matched warrior unfair in order to ensure that he is killed. This is the culmination in the TBR to a contentious meeting between the two and which ultimately results in a prediction of the TBC.
Looking at the misunderstandings of the Buan's Daughter passage there's two layers to the confusion, so let's start with the widespread assertion that this shows that the Morrigan loved Cu Chulainn and that she turned against him when he spurned her. If we actually read the text of the passage its not nearly that clear. He doesn't actually refuse her initially, he tells her it isn't a good time for him to "meet a woman" and only when she then offers to explicitly aid him in his efforts does he say that it isn't for sex that he's defending the border; this may be a reference to other occasions on which there are attempts to bribe him away from Ulster by offering him a woman, including Medb's own daughter. The Morrigan is also in disguise, having put on a richt or assumed form because he has of course already seen her in what may be her true form* in the Táin Bó Regamna [TBR] and in both the Buan's daughter encounter and subsequent 'Healing of the Morrigan' passage we see her appearing to him in very different disguises. Why is this? Because the two of them have an established and contentious relationship with each other, albeit one that is far more complex than simply adversarial. In the TBR for example when he realizes the woman he has been speaking to is the Morrigan he tells her that had he known the whole time they would have had a different encounter, implying he would not have parted so amicably from her. Similarly in the Healing of the Morrigan passage of the TBC when he realizes that he has healed the Morrigan he says that if he had known it was her he would not have done so. So why then is she coming to him at all? It is certainly odd given their previous interactions for her to suddenly go to him and declare her love while offering to help him in battle. One interpretation is that the scene isn't about seduction but is a test of Cu Chulainn's dedication to defending Ulster. From this view then the Morrigan isn't trying to actually proclaim her love but rather is seeing if he can be led into abandoning his post with the lure of a beautiful woman. He refuses and the two instead engage in battle, or at least she attempts to further test him by attacking him while he is battling the warrior Loch. I will note in fairness that some scholars do accept a romantic tone to this passage which leads us into the next point, which is the validity of the passage itself.
Although often treated as if it were ubiquitous to the TBC now, in fact this encounter is not found in other versions of the text, which more clearly and directly relate the Morrigan's attacks on Cu Chulainn to the TBR. For example this is from Dunn's version based on a text that doesn't include the Buan's Daughter incident but instead references back to the remscél of the Táin Bó Regamna:
"Then it was that the Morrigan daughter of Ernmas came from the fairy dwellings to destroy Cuchulain. For she had threatened on the Cattle-raid of Regomaina that she would come to undo Cuchulain what time he would be in sore distress when engaged in battle and combat with a goodly warrior, with Loch, in the course of the Cattle-spoil of Cualnge."
This has led some scholars, including Baumgarten in Éiru volume 34, to suggest that the insertion of the Buan' Daughter passage in that version of the TBC was a later one by scribes trying to explain the reason the Morrigan attacked Cu Chulainn in the story. This may reflect scribes who were unfamiliar with the remscél or, as Baumgarten further suggests, were trying to reconcile a misreading of one line within the TBR. This pivotal line is a comment by the Morrigan to Cu Chulainn (Yellow Book of Lecan version), "Is oc diten do baissiu atusa ocus biad" [I am and shall be guarding your death] which Baumgarten argues was a misrendering of "Is oc dídin do báis-siu atáu-sa ocus bia" that is "I am and shall be bringing about your death" (Baumgarten, 1983). In previous translations the error was forwarded that the word was a form of ditiu, which means protecting or guarding, despite that not fitting the context of the TBR passage which is clearly threatening and not protective in nature; Baumgarten instead suggests the correct term is díden meaning to lead to or bring about. Baumgarten's view has been accepted widely enough that it is given in the eDIL as an example of the word díden, in contrast to the older interpretations that rely on connecting the word to dítiu, however unlikely that seems in context. In this view the romantic overtones of the Buan's Daughter passage were created based on the assumption that the Morrigan had promised to protect Cu Chulainn in some sense and was appearing to fulfill that role, only becoming antagonistic when he refused her aid (Baumgarten, 1983). Even in this I might argue that there is less of romance at play and more a sense of guardianship, albeit one created through a linguistic misunderstanding.
The Buan's Daughter section has resulted in some modern readers and people interested in Irish mythology assuming that the Morrigan was in love with Cu Chulainn** and became his enemy only after he rejected her. I do not believe the text itself supports that assertion or that the wider interactions between those two figures can justify such a view, and think that there is ample evidence that the passage was indeed a later insertion to explain a misreading of the TBR. While this doesn't, obviously, negate the existence of the Buan's Daughter passage it should be taken into account when trying to understand the wider dynamic at play between the Morrigan and Cu Chulainn so that excessive weight isn't given to that single encounter and so that it may be understood within a wider context.
*its uncertain but as his encounter with her in the TBR is unexpected and does not seem to be one she prearranged the 'red headed woman' is the best candidate for the Morrigan's true humanoid form, in my opinion. She is of course a shapeshifter so most often when she appears in stories she is described as being in a certain form.
**I am perhaps understating this, as I have seen some extreme claims based on this passage including that the Morrigan was desperate to bear Cu Chulainn's child or was deeply heartbroken after his 'rejection'. Neither of these or the other outré claims sprung from them are supported in mythology or folklore but all seem to be rooted back in this single passage.
Baumgarten, R. (1983). Varia III. A Note on Táin Bó Regamna. Ériu, 34, 189-193. Retrieved from http://www.jstor.org/stable/30007756
Daimler, M., (2015) Táin Bó Regamna. Retrieved from https://lairbhan.blogspot.com/2015/03/tain-bo-regamna.html
Dunn, J., (1914) Táin Bó Cualgn
eDIL (n.d.) electronic Dictionary of the Irish Language. retrieved from http://www.dil.ie/
Faraday, L., (1904) The Cattle Raid of Cualgne