Inter-caste Marriage / Relationships or simply Inter-Culture marriages
For marriage related aspects, it is obvious that one should consider Shukra (Venus) the owner of the marriage or sex for all regardless of lagna-rashi or Chandra -rashi or whatever. And the Saptamesh (L7: Lord of the 7th house) from lagna to be considered for this discussion. Chandra-Kundali is very important for overall analysis and so is navamansh (D9) kundali for detailing of the marriage aspects. Chandra Kundali if it is pointing to completely opposite things than the lagan kundali then it is a “friction / sangharsh / tussle / takkar” of destiny (lagna) and the desires (Chandra). That is a separate topic in itself and quite complex one at that. So yes, Shukra from Chandra and L7 from Chandra are very important especially when it is Mesh or Vrishchik Chandra-rashi – as Shukra becomes the L7 from Chandra!
Different Castes or different culture, social aspects, language or religion or geography etc. This is represented by Raahu (usually the lower level than yours in above terms as considered by society – I don’t like to use caste as the word here -- lower or upper as I don’t believe in it!). Whereas, Ketu shows upper level of maturity, social circle, spiritual level and so on. It is obvious that Rahu & Ketu and their nakahstras would play a very important role in concert with Shukra and L7 for supposedly inter-caste or simply inter-culture marriages. Following are some of the formations that give rise to such marriages or unions / affairs whatever you want to call as per the country of origin and the “values” which are very different for different countries and regions.
(1) Shukra in Kanya (Virgo);
(2) Shukra with Rahu (or Ketu but more so Rahu)
(3) Rahu & L7 (Saptamesh) in yuti and in the 7th or 6th house
(4) Raahu in the 7th house obviously, a major indicator of inter-caste marriage or affair.
(5) Even Shukra or Saptamesh in 7th house in Raahu nakshatra could also show inter-culture affairs or marriage
(6) L5 in the 7th house or L7 in the 5th house could show love affair / love-marriage as it means in India) :) Companionship (live-in) before marriage
(7) Shukra or L7 in the 6th house could show inter-culture background family -- the partner would have similar upbringing as you have but parents have different one.
Different Variations as per planetary influences:
(1) Guru influence / drushti on Shukra-L7 would mean the marriage is not that socially controversial as they are raised with similar values & have a lot of things in common (say middle-class families in the cities in the same area and schools and colleges and so on)
(2) Mangal with or drushti on Rahu-Shukra or the 7th house could bring in too much exuberance and pre-marriage dhamaka! :)
(3) Shani influence or drushti or yuti could mean someone older or a bit too sincere as the partner.
(4) Uranus could bring in some weird / “un-orthodox” a bit too modern type of folks in contact! If you know what I mean.
(5) Neptune increases platonic love and sensory & sublime feeling for any planet it is associated with. Lata Mangeshkar has it with Shukra (art) and Dhoni has opposite Mangal (Sports).
(6) Surya will not let person lose his / her own standard & self-esteem and will not compromise beyond a limit. Or bring in some sangharsh or ego clashes etc. (Surya with Rahu Shukra or say in the 7th house away from Rahu Shukra or Shukra or L7).
(7) Chandra will bring in some emotions and feelings in it – it will ensure economic background is at least matching if not language or cultural. (Similar social class, economic background)
Now L7 from Chandra and the 7th house from Chandra is EXACTLY opposite to Shukra and L7 from lagna -- -this is a different topic. The timing is imp! Both effects can come in different stage of life or BOTH effects can co-exist in the same person to give one outcome. Or maybe one of the parent same background and the other different one and so on. If drastically different then it could mean multiple relationships (affairs, marriages etc) matching these descriptions from lagna & Chandra both.
D9 - -Navamansh Chart – it cannot override the D1 (lagna-kundali). It will just vary it. So if the main chart is having both good & bad stuff and D9 is all good – the bad of D1 might not have much impact / intensity will be lesser. 9 And So on) For example Shani is in the 7th house from Lagna & Chandra both and D9 has Chandra -Shukra in Vrishabh in the 7th house. D9 cannot override the effects of Shani in the 7th house in D1.