Someone reported a similar problem (false positive) but I'm not certain as to why that happens - NTT-Assemble is a pretty trivial (200 lines of code) program that extracts the needed bits from NuclearThrone's data.win file and combines them with .part files to make a new executable.
On my side Windows Defender with current definitions (1.223.2730) doesn't seem to be pissed by the executable anyhow.
You can always have the co-player send you the resulting "nuclearthrone" executable (~110MB) if concerned.