Listeners

They're definitely similar for their main subject around music and how it could be mixed with a action battle kind of story, the relationship of the two main character is also similar even though for Takt Op is a trio, I would say Takt op is basically an improved version of Listeners for the animation of the fights  

Both shows are written by Dai Sato, and it becomes pretty evident in the beginning. Both are shows about a boy living a boring life until a chance encounter with a mysterious girl leads him into an exciting adventure. Both shows have mecha-like objects and have Western culture on full display. 

Both shows has a similar concept with "boy-meets-girl" story, where main hero meets a strange girl, who has a superpowers. And also has a similar concept of the world, where there are monsters threatening to destroy humanity and robots that save people. 

Weird mecha powered by humans fighting weird creatures. 

Reset. Elfen Lied and Listeners are strangely similar to opening up their stories. Both give a story where an individual from some distant place ends up with their respective partner. Elfen Lied has Lucy with her split personalities to bring to Kouta. Listeners have amnesiac Mu pair up with Echo, hoping to get her memories back. Both are good action anime with Listeners featuring mecha, Elfen Lied having a more psychological atmosphere to it.  

Need more musical preference? I thought you can arrived here and sip the tastes. While Listeners using amplifier as an Equipment, Akanesasu use some Vinyl disc player and the stylish cassette player as their main power. The elements of music really obvious on these twos show. Look, even the both of the MC had and headphone on their accessory. Ah, another one, its about the radio frequency waves, or something. These twos had it. While Listeners used it to strengthen the power of an Equipment. Akanesasu Shoujo used it to changed between the parallel world. Feels weird? Just watch by youself. And feel that music preference i referred before. Also, be careful with the relations between the twos MC. Both show had a pretty messed up relationship with mind-blowing end. The battles with those twos felt pretty messy too. So, yeah, you had been warned.  read more 

Both shows are original mecha anime that try to bring something unique to the table through their world building. While Planet With accomplishes this aim significantly better, Listeners has the more attractive premise. Both shows seem to struggle with pacing at times, but in opposite ways- with Planet With coming dangerously close to growing stale early on, and Listeners erratically hoping from plot line to plot line. If you want two interesting but flawed original mecha series, these will be right up your ally- but if you can only watch one it should certainly be Planet With.  

Both have similar method of abstract multi plot line storytelling with healthy dose of symbolism. 

In both anime a boy who is obsessed with technology and has no life goal, meets a foreign girl and joins her adventure.  

The opening sequence of the barren landscape in HMC immediately reminded me of Listeners' setting. Both series also have a major focus on music, and mecha with highly stylized characters.