The fifth Japanese meeting on host-transposon interactions, titled "Biological Function and Evolution through Interactions between Hosts and Transposable Elements (TEs)," was held online on August 26-27, 2021. The meeting was supported by National Institute of Genetics and aimed to bring together researchers studying the diverse roles of TEs in genome function and evolution, as well as host defense systems against TE mobility by chromatin and RNA modifications and protein-protein interactions. Here, we present the highlights of the talks.