Dual crosses over with Pretty Sammy once in the OVA, and several times in other materials including the DVD case inserts and AIC backed mangas…. so if there was anything to connect there, it’s Dual -> Pretty Sammy.
Now since years ago, Kajishima has reintegrated Dual by way of GXP, not just the mechanoid, but also through alternate versions of Dr Sanada, Mitsuki Sanada, and Dee.
So it’s more like:
OVA/GXP – Dual – Pretty Sammy
El Hazard also had cameos like posters to Pretty Sammy, I can’t recall any characters showing up in person, but there’s been a lot less there to tie it to anything Tenchi.
Geminar has some nods to Dual in the theme or designs, after all KM himself said that Geminar was what he had originally intended Dual to be. The Bioroids, dimension hopping, mech designs, powering a robot through will, some other minor things, are related to stuff showing in Dual, but other than being connected back to the OVA again, no major connections.
So it’d be more Geminar – OVA/GXP – Dual – Pretty Sammy.
Tenchi Universe doesn’t have anything currently to tie it to Dual, Kiyone showing up at the end of the OVA of Dual is from Pretty Sammy, where she exists there.
