Both of these anime:
- Have plots that revolve around the human race's symbiotic relationship with giant legendary creatures who are used as ultra powerful weapons.
- Have grandiose endings set on a huge scale with lots of death
- Are thematically similar e.g. fear of death, betrayal, war etc.
- Have main characters much younger than their comrades who are yet to truly mature
- Have the celebrated Hideaki Anno deeply involved in both projects
The style of Ryuu no Haisha certainly reminds one the old Ghibli movies. It's based on some old Asian legends and myths but somehow modified to the nowadays or recent world and society. While in Laputa we have the flying castle, in Ryuu no Haisha we have the dragon large as a castle. There are people involved seeking it's power for their own purposes and there are also people trying to protect it.