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.
Both anime are military space operas with a large cast spanning a long time period, in which two factions of humanity fight over political differences and domination of the known universe. Both tonally resemble a dramatized history presentation, in which the political leaders, the military strategies, and the social impact of events are important story points. There are large scale battles in space and urban warfare in both, and backstories for the main characters from childhood to young adult. Both "main main" characters, Reinhard von Lohengramm and Casval Rem Deikun, are blonde Machiavellian prodigies and military strategists. There are many more parallels within the two