Ushinawareta Mirai wo Motomete

High school students and their future selves change the future through changing the past events by the aid of some time travel/parallel world concept in order to save their friend from a destined death. 

Both Waremete and Orange have some kind of time traveling concept, have some kind of school setting and death that is avoidable, main characters have some kind of deeper itentions, why they are doing what they are doing, have whole traveling concept is based on science.  

-Both series set in high school -Both series they try to change the past after a tragic event -Both series explore the concept of regret -Both series involve some sort of supernatural occurrence to deliver a message through time 

Both have something to do with one of the character who will die, and it will involve something from the future that will save that character. 

Both shows mix sci-fi with ordinary school romances, as there are hidden twists revolving around time travel, and going to the past to prevent the death of a friend  

Both of the anime tells a story that uses the idea of regrets. The story sets in a highschool and a focused on a love story between some highschooler. The story then expands to tells us a the same story with a different outcomes based on the action that the character takes in the past. Both also uses different timelines to tell us the main story. 

I'ts also about time travel and paradoxes. Watching it immidiately made me think of steins gate. 

Steins;Gate contains ideas and characters similar to Ushinawareta Mirai wo Motomete. Character-wise, both shows maintain similar casts. Besides the main character, there's the male, slightly weird best friend, the childhood friend that the MC wants to protect/save, the tsundere that's in love with the MC, and a time traveller desperately trying to alter the future. With regards to plot, both deal with Time Travel. I would recommend Steins;Gate to anyone who enjoyed Ushinawareta Mirai wo Motomete, but Steins;Gate is infinitely better, and would likely leave a watcher going the other way unsatisfied. 

Both involve time travel and trying to stop someone from dying over and over. 

The plots of Alternate realities existing together and tends to converge if any deviation made with past. 

Both of the anime is about time travel and explains its theory in detail. Their own concept of time travel are interesting. Both anime has characters that desperately try to save someone by going through countless time loops. 

Astronomy Club members solve mysterious events around them. A mysterious object/person is the key to stopping it. Supernatural events are occurring that changes their lives forever. One series is based on a manga while the other a visual novel.  

Similarities: Both have main guy as MC, both have dark and tragic undertones, and have this Astronomy Club which is also the place where most of the scenes are happening. Both are also harem-like animes that has this main girl which is the love interest of the guy MC. 

A casts of characters who met each other through an astronomy club. Both of these show has quitr a dark undertone to it's drama, with a touch of romance and supernatural aspects in it. 

Both of these shows include a white/silver haired female protagonist traveling back in time; this decision being made by another character in the show. Another aspect these two have in common is the fact that there is a group of other characters who later on become friends with the female protagonist. Romance is prominently seen in both series. Both incorporate the school setting.