Experience Tumblr like never before
I've talked about codependency and how it presents in Hunter x Hunter, and now I want to talk about how it presents in Dungeon Meshi - specifically between Thistle and Delgal.
Thistle, from the start, is in a perfect place to be taken advantage of and manipulated. He was taken from his family as a child, and he knows nothing about his past, not even his name. His sole purpose is to be there as a fool to entertain those with power. Delgal's father names him and raises him like a "son" and a "brother" to Delgal...but let's be honest, there is nothing normal or "brotherly" about how Delgal and Thistle interact here:
Thistle is not an equal with Delgal. From Delgal's perspective, Thistle is court magician and confidante, the one who can save his life and his kingdom. I certainly don't see Delgal considering Thistle a "friend" or member of the family. Perhaps when he was younger, but definitely not as an adult. Some of the earlier interactions between Thistle and Delgal as the latter grows up might have been sweet - sneaking food to share, talking about Delgal's marriage - but that sweetness quickly turns sour when we see how Delgal treats Thistle when the elf cannot be of use to him.
There is a tremendous amount of pressure on Thistle's shoulders. He knows Delgal's love for him is conditional; we can argue that Delgal yelled at him in a moment of desperation, but the fact that Thistle later feels the need to apologize (for...not being able to make Eodio defy death?) tells me he's used to asking Delgal for forgiveness where there is nothing logically to forgive.
Delgal, however, offers heaps of praise for Thistle when he keeps his kingdom and people safe.
Delgal needs Thistle to maintain rule of his kingdom and keep Eodio alive, and in turn, Thistle needs to be needed to feel fulfilled and useful. Thistle is Delgal's codependent, and Thistle has misconstrued putting aside his own wants and interests (his Adventurer's Bible page lists his likes and dislikes as "Nothing") in favour of serving Delgal and only Delgal. Thistle craves the affection he receives in return, and who can blame him? He has no family to speak of, no connections to the world outside of Delgal. Praise from Delgal is all Thistle lives for - and so he pours himself into creating the dungeon, keeping his people safe to the point of immortality.
So when Delgal and Eodio begin to talk about leaving, it's understandable that Thistle reacts so violently. If he can't protect his people, he can't earn Delgal's affection and praise. He is too deeply entrenched into the role of dungeon lord - the role of Lunatic Magician - to see that the dungeon is falling apart, and that Delgal probably long regrets asking Thistle for help.
Thistle is so obsessed with protecting Delgal and earning his love that he maintains this obsession for an entire millennium. Mithrun eventually tells him that Delgal is dead, to set his people free, and Thistle is in complete denial. He continues to search for Delgal even after learning the truth from Mithrun. He is so panicked about finding Delgal and proving that Mithrun is lying that he is driven to self mutilation.
Thistle's love for Delgal is not "true" love - it is obsession. But, in turn, Delgal's "love" for Thistle is not true love, either. Delgal would not have placed blame on Thistle for his son dying, would not have praised his use of dark magic, would not have placed the weight of his life on Thistle's shoulders...had he truly, purely loved Thistle. And I think Yaad knows this, because, when Thistle finally "reunites" with Delgal, he gives Thistle the apology and accountability the elf never got at any point during his life. He's sorry he made Thistle worry, and he's sorry he placed so much weight on his shoulders...those are things Delgal likely never said to Thistle at any point in time, but that Thistle deserved to hear after a thousand years. And I think it's very telling that the apology he got from "Delgal" isn't from Delgal at all - because the real Delgal probably wouldn't have apologized to Thistle in the first place.
I know there's some debate about whether or not Thistle is dead at the end of Chapter 96. But I am of the belief that yes, he is - that after finally being freed from the burden of needing to earn approval and protect everyone, and hearing Delgal apologize for it all, Thistle is at last able to rest peacefully.