Ginga Eiyuu Densetsu, Mobile Suit Gundam: The Origin Recommendations
Both Gundam Origin and LotGH deal with war and politics, and have a really similar vibe. Char and Reinhard are similar characters, as they are both tactical geniuses and have hidden agendas. Furthermore, the space battles in Gundam (episode 5) reminded me a lot of those in LotGH.
Both Char and Reinhard are ambitious and Machiavellian characters. Both stories follow their development from precocious children to vengeful young adults and remarkable military tacticians.
Of course, both stories take place in space, with large scale space battles.