Eh, considering that there's pretty much a war going on between the A-rankers, who Eunju gives her dice to is definitely Mio's concern. It's every A-ranker's concern. And considering how this conflict is affecting pretty much everyone else, it's everyone's concern. While she's trying to do what she perceives to be right, everyone else is trying to stay alive throughout this ever-expanding conflict. If Mio thinks Eunju's giving the dice to someone that might pose a threat, it'd be completely reasonable for her to decide to stop her. It would've taken little effort for Mio to take the dice from Eunju and increase her own and the Defence team's ability to complete their tasks and protect those around them, some would say that would've been a completely justified act. How Eunju feels is important only for as long as those around her tolerate it. It's a weapon that is almost certainly going to come into play at some point, whether Eunju uses it, has it taken from her, or hands it over to someone else. The idea of prioritising Eunju's 'right' to decide the fate of a weapon she took off some dead body in the face of the potential effects this dice can have is actually ridiculous when you put it in perspective.
Of course you are right.
Then again, I was trying to see things from Eunjoo's perspective. In her eyes i) it's by no means clear that Mio and Dongtae are the best option to ensure survival (of whom?, to begin with); ii) Mio stopping Eunjoo based on her own judgement of what is a threat is definitely a selfish decision in that Mio believes she is the one who can make that judgement.
But you are right. This is ultimately a matter of power: Mio
can stop Eunjoo, and there is nothing Eunjoo can do to stop her. So morality, or protecting people, or having or not having a plan to stop X, has little to do with the decision to seize Eunjoo's Dice.
Much store is set on the decision to belong to a team, but there's the catch: while belonging to a team means fulfilling the role apportioned by X in exchange for a reward, A-Rankers can have agendas of their own and decide to protect people while being Neutral or even in Attack (team-killing, anyone?). Given that Attack can earn Dice from defeating other Dicers during the quest and Defence cannot, I personally would find belonging to Attack the better option to protect the school.
In other words, especially from the point of view of Eunjoo that all Dicers are playing to X's tune, the decision of protecting people has
nothing to do with which team one belongs to. Mio has the "right" (in that she has the
might) to seize Eunjoo's Die to ensure
her own and Dongtae's survival... just as Eunjoo has the "right" (if she is tolerated to do it as you put it) to give it to Taebin if she believes this is the best way to have a shot at defeating X or if her own judgement says it is the right thing to do.
So I would contend that the very idea of
prioritising someone's right is, forgive me, ridiculous. The priority is in the power. If we could choose a truly impartial, detached judge of what is moral and what is right - which is impossible -, the natural rights to dispose of one's property as one sees fit would certainly take precedence over vague considerations like what is
practical - something neither Mio nor Dongtae are in any position to judge. (Neither is Eunjoo, of course, but the Die is hers: even X said so.)
This sentence of yours is curious: "While she's trying to do what she perceives to be right,
everyone else is trying to stay alive throughout this ever-expanding conflict." (emphasis mine)
So I suppose Eunjoo is
not thinking of her own survival, or that it is not as important a consideration as everyone else's survival. Because you know, if we rewind the clock a little, heeding Eunjoo's opinion on Dice would have been the best option for "survival" (more on that later).
If you still think I am beating around the bush, let's take your opening lines: "considering that there's pretty much a war going on between the A-rankers, who Eunju gives her dice to is definitely Mio's concern. It's every A-ranker's concern. And considering how this conflict is affecting pretty much everyone else, it's everyone's concern."
This is only trivially true. It's the same as saying that when a house is burning, what the neighbour decides to do with their water hose is everyone's concern. However, this is also true of all Dice in everyone's possession, include the ones that can be seized by killing the person. If it is okay to seize Eunjoo's Dice to ensure people's survival, why, the best option would be for the B-Rankers to round up all A-Rankers they can find and restrain them. Or to offer Taebin on a silver platter to Hood. These may be more extreme actions, but they would certainly be more effective than changing the possession of a single Die, even more so because X can easily make things much bloodier regardless.
Since arbitrary acts - or any acts to be honest - cannot be justified
a posteriori, if Mio decides to seize Eunjoo's Dice, it will be because she wants to, not because she is in any position to decide - judiciously or otherwise - what is the best course of action for dealing with her Cloaking Die. After all, if we go by what you say and Mio decides to take Eunjoo's Die, and later something bad happens because of this decision, your reasoning suggests Mio would be at fault. But this is nonsense, and so the opposite - not seizing Eunjoo's Die and this later leading to a good outcome - also wouldn't vindicate my contention that Eunjoo has the "right" to do what she wants with her Die. The issues are not connected at all.
I'll leave aside the fact that seizing a Die from someone against their will is no trivial business. We all know what happened when Taebin tried to do it to Dongtae in chapter four. In the present case, the gap in power between Mio and Eunjoo is even smaller. Do you really think things would go smoothly?
Incidentally, I doubt Eunjoo is thinking along these lines, but surely, given what you are saying about how impulsive and naïve Dongtae is, giving her Die to a person who has no Dice points to activate either Skill, or to a girl whose main skill is Defensive and not Offensive, would be the height of folly in my opinion.
And if one contends that Dongtae at least is doing something to protect the school while Taebin is just sitting around - indeed, one would have a point. I'm not saying that giving the Die to Taebin would be the better option. And that is, so far as we know, not what Eunjoo is chasing him for: she wants "to ask him something". Then again, neither Eunjoo nor Mio have the knowledge of Hood's true intentions (killing people until Taebin shows himself). From Eunjoo's point of view, this may well be another event orchestrated by X, and in any case Dicers have brought this upon themselves, Dongtae included. So there is
no categorical imperative that Eunjoo ought to give her Die to Dongtae, at least as of now.
And since we're dealing in the matter of survival, I return to my previous question: survival of whom? Let's consider possible answers:
1) Of oneself
This is useful because it is no-nonsense. When considering self-integrity, one can decide on things in a straightforward manner. For Mio, seizing Eunjoo's Die is a no-brainer, since there is no other way of earning Dice for Defence during the War. But you seize her Dice and then... what? There are still seven Dicers on Attack, and four quests to go.
From Eunjoo's point of view, her survival would be much more assured if she surrendered her Dice to an A-Ranker peacefully in exchange for being spared (and who would kill a Non-Dicer just for the heck of it?). The second best option would be to find a strong A-Ranker who would be willing to offer her protection, for sentimental or practical reasons. Right now, the best one is Taebin. And the third option would be to become an A-Ranker and using the remaining Dice points to become invisible when needed.
2) Of oneself and the ones that are precious to one
For Mio, nothing changes here. However, she doesn't know it, but giving Dongtae a Cloaking Die will make him a direct target to Muyoung, which he isn't right now.
For Eunjoo... ditto.
3) Of as many people as possible
Things get murkier, but from Mio's point of view, helping Dongtae is the best route. Whether stealing Eunjoo's Die contributes to that end is debatable, but I'm sure Mio could reasonably come to that conclusion.
For Eunjoo... it's anyone's guess as of now.
So I stand by what I said. Eunjoo is not wrong, and Mio is not right. Add
might to the equation, and any outcome becomes possible.