RELATIVELY LARGER EXISTENTIAL QUESTION OF THE OTHER
The existential question of the self leads to the existential question of the other. Either one may be a larger question, except that the other lies further beyond one's realm of experience.
One would, for example, study the existential meaning of another person, except that there is a more immediate pressing concern of one's own existential reality.
But, let us say that one may certainly consider the problems another person might face in their own existence. They are theoretically comparable realms. Except they exist as different modes.
So, let us pursue the idea that the questions of self lead to the questions of other. This could produce an ontology of otherness even when the other may not be understandable or real on the terms of the self.
For example, if the self wants to commit suicide, this produces resistance in the other, which suggests that there is something wrong with committing suicide. But, when the self loves the other, the other responds with weakness or mockery, suggesting that there is something strong or funny about the person engaging in the love of the other.
In any case, the other appears to exist as a physical response in the mostly physical realm, and as a spiritual response in the spiritual realm.
However, the important thing to remember is that the questions of other are derived from the questions of the self.