Without index changes, performance improvements might be obtained by:
OPTION (RECOMPILE) query hint to get a plan optimized for the current value of any parameters or variables. This could also result in simplifications, for example by removing the need for a 'dynamic seek' as seen at the far right of the plan (constant scans and merge interval), and removal of startup Filters.
Ensuring statistics are representative for all tables in the plan. This may affect the shape and content of the plan selected by the optimizer.
Breaking the query up into smaller parts that are easier for the optimizer to assess and plan for individually. There are a large number of joins, so the chances are high that cardinality estimation errors will occur, even with updated statistics. Use one or more temporary tables (not temporary variables) to store parts of the query that execute efficiently. Natural places to break the query up are just before a sort, or just before a performance-affecting cardinality misestimation occurs. Done well, saving a small number of small intermediate results sets in one or more temporary tables can produce tremendous performance and stability improvements. The temporary tables can also be indexed without changing the schema of the main database, if this proves beneficial.