During the second world war the two siblings, Seita and Setsuko, are suffering because of their mother's death. They are taken to the house of their friendly aunt who gladly accepts them, as she promised to her sister. However, as japan is drawn more and more into the war, food and supplies are growing thin and there is almost nothing left. The aunt, despite her moral, start to turn into a cold person who makes the two siblings leave the house and survive by themselves.
They are both about siblings struggling to get through a disaster.
Hotaru no Haka follows 2 siblings struggling to keep alive during a war and Tokyo Magnitude 8.0 follows 2 siblings struggling to get home and stay alive.
Both are really beautiful and sad animes with lot of emotions.
I highly recommend you watch both.