Vandread

Both are about Mechas, and combining Mechas.. and nobody knows/understands anything at first.. Rasen Energy for Gurren, and the Paxis System for Vandread. Both main characters also have low self esteem in the beginning, and realize the importance of friends later.. However, Vandread is not as crazy and random as gurren lagann.. and it also has a more developed and realistic plot. unfortunately, vandread is missing Yoko, so i wont recommend it for hardcore yoko fans. However, it has 3 main female characters, and another 1 maybe who make up a lot for Yoko.. a hyperactive redhead, a silent, coldhearted-looking bishoujo (yuki nagato comparison), and a weird tsundere blondy.. Overall, i kind of prefer vandread over gurren.. gurren is intense and too random (mainly because of kamina).. while vandread makes good sense and gives u something to think about.. And i prefer the girls in Vandread over Yoko too.. the only thing i really like about Yoko is her skeleton hairpin.. lol..  read more 

the story plot is the same, two races that hate each other and tries to kill each other, but later combine power to kill the enemy that tries to wipe out their planet. in tengen its the humans and beastmen, in vandread, its man and women. similar story plot oh ya theres a lot of mecha in vandread too, so much better than tengen must see  

In both the main character is a simple kid that soon appears to be in the centre of the universe. Both are Mecha and take place in the future. They are of those type of anime that get more and more exciting with every episode and pump you with adrenalin leaving you asking for more and more. 

Once Vandread introduces the empire's enemy, you will understand. From the tongue in cheek humor to the playful mockery of Shounen mecha norms, Vandread is a great segway from planet hurling goodness XD. Just like TTGL, Vandread seemingly accidentally hits the right chord time and time again, delivering emotional moments many 'serious' animes fail to execute. Where TTGL made you a man, Vandread will show ya what to do with it. Also, you're less likely to get an eye-roll from the girlfriend. ;) 

This is an easy one. Both are mecha anime that have space battles, fanservice, combining mechs, comedy and romance. The main characters are both very short for their age (though Hibiki is a lot more abrasive than Simon) and end up forming a bond with an outlandish girl who is very kind and helpful (Nia/Dita). Humorously, Hibiki's dub voice actor, Tony Oliver, also serves as the narrator in the dub of "Gurren Lagann". Essentially, if you liked "Vandread", you will love "Gurren Lagann". 

Same war in space. We have funny male protagonist, 

Both are harem + mecha anime with your typical anime girls. And all this girls eventually fall in love with protagonist. The only big difference between anime is that isekai is taking place in fantasy world, vandread - in space. 

Both series contain sci fi themes and involves the characters protecting what they believe is dearest to them. Both series has a lot of emphasis on the characters and how the mature over the episodes through battles, life, and experiences. Both series also contain similar art style with drama, comedy, action, and later romance.  

Come on...HOW is this not already the number 1 recommended for vandread? Outlaw star and vandread have a far more similar plot than anything else on here.  

Similarities - Mecha: Co-pilot is of a opposite gender - Characters' rules and ideals set by "Papa/Grandpa/Grandma" - Fighting against mysterious forces 

The theme of mecha, sci-fi, themes and women are involved in part of both series. There is mystery surrounding the background of both series as drama develops between characters. Additionally, the main protagonist has a destiny and mysterious connection. Speaking of which, there is also romance in both series involving the main protagonist.