Identification: Older Sci-Fi anime involving a parallel universe where a group of elite fighters fight their alternate universe counterparts

Question

A while ago I came across a reddit post of which the topic I have now forgotten, but one of the comments mentioned an anime that was available subbed on YouTube. I watched that anime and remember enjoying it, but I cannot seem to find it again despite rigorous searching.

Plot Details

I don't remember many details, but here's what I do remember:

• It was set in a futuristic sci-fi world, probably a future Earth
• It involved a group of characters (I think 5 of them) that were part of an organisation fighting against a parallel universe/world threat
• These two worlds had somehow been connected due to the year that it was (maybe 2060 or close to?)
• The protagonists regularly entered a sort of "middle dimension" that matched their world but was more of a battle field and wasn't actually their world
• They had to fight against the alternate world versions of themselves
• There was a technology or some other thing that was "gifted by the gods" that could increase the development of a certain item by many years (an example is taking a normal gun and then turning it into a futuristic gun)
• One character used this advancement thing on themselves during a critical battle later into the season to give them immense power, but it ultimately ended up also killing them not long after since it aged them past their death
• I think the end of the anime involved some discussion with their alternate universe selves in order to discuss the fate of both their worlds
• At some point during the anime I think one member of each world got sent to the alternate world and you get to see that there is a severe contrast between the main protagonists' world that is fairly well off, and the alternate world that is struggling to survive

I think the anime was an older anime, as the art style definitely seemed that way. Those are all the details I can remember.

Answer 1

This is Gunslinger Stratos: The Animation.

The story revolves on a group of gunslingers, each from the two universes (Frontier Stratos and the 17th Far East Imperial City Management District) who participate in Operation Stratos, particularly on a group of four childhood friends: Tohru Kazasumi, Kyōka Katagiri, Kyōma Katagiri, and Shizune Rindo, who all must confront their own flaws and differences when they battle their alternate selves from another universe in order to survive.