Besides that something like this https://de.wikipedia.org/wiki/Erdgasleck_in_der_Nordsee could also lead to a tsunami if it caves in.
Considering how many we have there it's not that unlikely:
https://en.wikipedia.org/wiki/List_of_oil_and_gas_fields_of_...
Power plants are built according to the requirements of their location and history shows we fail in getting all the risk
Not to mention corruption and botching.
Which company would you trust to built and operate these power plants?
Vattenfall, Shell, Siemens, Facebook, Apple?
Edit: Alternatively Die Schwesternschaft des Heiligen Strahls, äh Scheins.
There is also post-glacial rebound in northern Germany with several fault lines, one of them roughly between Kiel and Lübeck. Where parts of Denmark, Sweden and Norway still slowly rise, while the outer parts bordering Northern Germany slowly sink, 'scratching' against it.
Also several large salt domes, producing sink holes which can be seen as lakes today. Interestingly, some of these are being explored today as energy storage solution, what could possibly go wrong?
edit: Besides that, flooding. Again and again
https://de.wikipedia.org/wiki/Liste_von_Sturmfluten_an_der_N...
Pick your 'fiction or fantasy' ;->
Because heavy earthquakes in Germany are unlikely the standards for german nuclear power plants aren't planned to withstand one because the planning is accordingly to the dangers of the location.
And that is the problem. We are building something that has to last decades if not centuries and if we miss something the damage is severe.
For example before satellite imagery ships were built according to the normal distribution of waves which said large waves are rare, freak waves nearly impossible. Stories about freak waves were even often dismissed as exaggeration or sailor's yarn. Nowadays we know freak waves happen a lot more often as we thought and ships are built accordingly but older ships have problems if a freak wave shows up or they simply sink.
Mind you - nobody thought we got tsunamis in Scotland:
https://en.wikipedia.org/wiki/Storegga_Slide
Just to make clear: I'm completely comfortable with nuclear power and I live reasonably close to the remaining operational nuclear power station in Scotland:
https://www.antipope.org/charlie/blog-static/rants/nothing-l...
And still there were only a handful of deaths directly caused by it.
More people die because of wind turbines every year.
Nuclear deaths is 90 per TWh
Wind death toll is 150 per TWh
Solar 440/TWh
and leading the pack is Coal at 100000/1Twh produced
The question is, as always with nuclear: Do you want constant, verified, 100% certain deaths every day or do you risk a larger death toll that may or may not happen some time in the future?
That's like comparing death by train accident or plane accident. Planes are better per kilometer but worse per hour.