Kidou Senshi Gundam Thunderbolt

-Both are set in space, but not outside solar system -Both have great jazzy soundtrack -Both are stunningly animated 

Bolth are mecha anime where the cast are seen as mostly expendable soliders. Bolth emphatise comradery between the cast. Characters, animation and ost is great in bolth. Thunderbolt requires little context from other gundam anime making it a great geatway into the franchise. 

Aside from the main story, they serve as spinoffs to divulge more into world building and lore by exploring themes of the main stories into a deeper setting. MCs are ruthless soldiers loyal to the government conducting their duties on the battlefield with a powerful mecha that is said to be feared amongst the enemies. Music in both shows contain jazz themes that make the stories much more darker than the other entry. Aside from that, the animation is top notch in a limited series with small amount of episodes. 

Both anime... ...have stupendous animation, taking its time to show how the mobile suits work and how are destroyed. Also modernizing the designs of the original series. ...are short spin-offs of the one year war, in the universal century, depicting a minor front of the larger war, that is notable for the difference in scenario and equipment deployed. ...take a more realistic and gritty aproach to Mobile Suit combat, with emphasis in equipment, tactics and strategy. ...follow characters, and dynamics among them, in both sides of the conflict portraying in a relatable and human way. ...have romantic subplots, albeit managed in different ways. ...have people who are devastated by the consequences and destruction of war, and people who enjoy the fight and think only about winning. ...have nice people in Zeon.  read more 

MSG Thunderbolt is basically LoGH in miniature: -Political confrontation in space between two human factions -Main leads are somewhat similar in personalities, especially with Reinhard and Io Fleming -Lots of fights in space with battleships/mechas. 

* Both are short series that are spinoffs of a larger narrative from iconic mecha series. * Both feature top-shelf art and animation for their respective eras. * Both feature excellent soundtracks composed by former members of The Seatbelts. 

Both are incredibly dark shorter Gundam series taking place during other shows in their respective timelines. Both are fun, easily rewatchable rides, with MS design ranging from solid, to great. Both have very memorable characters and moments, and serve to further flesh out the conflicts of each series