Put crackers in large resealble plastic bag, and crush with a rolling pin.Pour crumbs into a bowl, add sugar and butter. Press the crumb mixture into a pan (or cup).Chill for 30 min.
Beat the cream cheese, add agar-agar mixture (mix agar-agar with cream), yoghurt and lemon juice.
Pour the filling into a crust. Add orange. Chill for 4-5 hrs.