Tenchi Muyō!
Tenchi Muyō! GXP
Paradise War
Isekai seikishi no Monogatari
You can add it since they are all from the same universe and tenchi muyo is already ending with its 5th season where it tells the events of kenshi.
Isekai seikishi no monogatari is definitely what I would pick out of the options available. Never see any fics with it. Not a big fan of mech anime but this is the exception.