Dasein is a being that does not simply occur among other beings. Rather it is ontically distinguished by the fact that in its being this being is concerned about its very being. Thus it is constitutive of the being of Dasein to have, in its very being, a relation of being to this being.
Martin Heidegger, Joan Stambaugh, Dennis J. Schmidt (2010). “Being and Time”, p.11, SUNY Press