Tengen Toppa Gurren Lagann, Little Witch Academia (TV) Recommendations
Akko and Simon have very similar character arcs. Both shows focus on believing in yourself for power. Magic is very similar to fighting spirit. Little Witch Academia contains references to Gurren Lagann. Some shared staff between both shows since Trigger is made up of former Gainax employees.
These series have a similar feel to them which made me want a cross-over