If you're looking for anime similar to Kurogane no Linebarrels, you might like these titles. All recommendations are made by Anime-Planet users like you!
Sogoru Kyo is a normal high school student with great passion for the things he holds dear. In fact, his love for swimming is so great he is attempting to single-handedly keep the team alive. However, his life takes an unexpected twist when meets a strange girl at the pool whose existence shows him an enemy force that is threatening the very existence of humanity. These beings known as GARDS-OMS seek to eliminate humanity and take Earth for their own. His choice is to live as he has been, or take a place in the cockpit of a mecha to stop the extinction of humanity. They often say the truth will set you free, but in this case the truth may destroy Kyo and leave his beloved hometown without the hero it so desperately needs.
The shows are equally as good and have a lot of the same elements. The main characters are both naive young men who want to make a difference and yearn for a world that they believe is perfect. There is a girl who comes out of nowhere and introduces the young man to the means of getting his "perfect world" although those ideals are slowly shaped to be a more fitting way of seen the world instead of the young man's naive version of what "justice" is. And (I have to say it), of course both of them involve giant robots fighting to the death.
Two centuries have passed since man began colonizing space. The Earth Federation, which governs the human race, has known of the existence of hostile aliens for the past seven years and has been preparing for an invasion. However, while they see military force as the answer, others would rather surrender to the aliens in exchange for their lives. Taking advantage of the confusion, an organization called the Divine Crusaders declares the Earth Federation unfit to protect the planet and plunges humanity into a bloody civil war. Now only a small band of heroes - pilots of experimental super robots - can save the day. Pressured by a desperate Earth Federation government and faced with conflict on all sides, can this mottled group of individuals find the courage to not only end the civil war, but to also defend all of humanity?
The underlying plot from Kurogane no Linebarrels is taken from Super Robot Wars: OG Divine Wars. Both are about two factions trying to save the Earth from an outside threat their own way, one through global domination, one via an alliance.
Of the two shows, Linebarrels has more modern CG while SRW has a better range of mecha. I'd say SRW is superior as the characters are more likeable and the mecha designs more impressive and it just seems more epic but it'll be up to indivual preference, some will no doubt prefer the harem-style subplot of Linebarrels... To each their own but if you like one you should enjoy the other.
Half a year has passed since Sousuke Sagara took up the job of protecting Kaname Chidori and has started living like a normal teenager for the first time. A former child soldier, his view on the perils of everyday life is highly unconventional and in frequent need of violent adjustment; Kaname can only hope her endless assault will eventually get him used to normal life. But a shadow looms over their happy days as Sousuke's employer, the private army called Mithril, is attacked by a new unknown enemy. Suddenly outgunned, can Mithril afford to keep one of their best playing around?
In the year 3567, the human race has lost their once technologically-advanced world due to their negligence with the planet. Now, their lives are in jeopardy when machines known as Gardeners are sent from the moon to destroy all mankind. Tokito Aizawa is a hunter who makes a living by destroying Gardeners and selling them for parts, but his life otherwise is fairly normal – until now. One day, while in town, Tokito meets a mysterious girl named Tea who calls him by the name "Koichi"; and in the midst of confusion, a large group of Gardeners suddenly attack the city. Tea then grants an unseen type of machine called "Silver" to Tokito – a machine that might be mankind’s best hope of evading destruction...
In both cases for the male protagonists, soon after meeting a strange girl with missing memories, they begin piloting an outstanding mecha with unmatched power on the side of justice with her. While the leading male character from Gin-iro no Olynssis has a nickname of Koichi, in Kurogane no Linebarrels, the head male character’s name is also Kouichi. How more alike can you get when it comes to characters and introductory plot?
Long ago there was a battle between angels and humans, which ultimately ended with the angels’ retreat. Twelve thousand years later, the angels have become active again and have begun harvesting humans for nefarious purposes; and only the pilots of the ancient mecha known as Aquarion are able to oppose the angels' tools of war. The pilots have special powers, but the secret to defeating the Angels once and for all lies with the reincarnations of the two beings who defended humanity against the Angels in the past: Apollonius, an Angel who turned his back on his kind in order to protect humanity; and Siren, his human lover. Only Apollonius can awaken the true strength within Aquarion that is needed to defeat the angels; but who is the reincarnation of Apollonius?