What is required for a manga to get an anime adaptation? I'm reading Koe no Katachi and have been hoping for it to be animated. It looks like it's getting more popular. However, it makes me wonder what requirements should be fulfilled before they decide to create an anime based on a certain manga in general.
There is no written path, but there are several factors and steps that must happen for that:


Fanbase


The overall reaction to the manga, the volume of internet traffic it generates (fan-art, forums, discussions, fan pages, fan fiction, even porn of the main characters).  
Are fans cosplaying as the characters even before anime?

Connections and reputation  


The reputation of the mangaka. For example, I doubt any new manga by Rumiko Takahashi (for example) is NOT going to become an anime.  
Who the mangaka and the manga producers/managers know. Sometimes the hardest part is to put your work in front of the right eyes. It's all in the pitch.

Possible merchandising and target audience


Can the manga become a toy line? Can you sell costumes of the main characters?   
The target audience (gender, age, genre) spending power.

Series health and controversy  


Is the manga series long enough? Are the arcs and plots interesting? Are the characters well developed and of enough depth?  
Is there any group that will get grossly offended if the manga becomes an anime? Remember that printed media is pulled by the reader (you have to actively persuse the media) while audiovisual media is PUSHED into the viewer.

Competition and market mood  


Is the manga a mecha manga, and it's on its peak during a new Gundam season and yet another Evangelion Retcon?  
What was the reaction of fans to the animes of the same genre that aired in the previous seasons? Are they craving for more of the genre or had they have enough?

Releases and versions  


Is the series already compiled into tankobon? Is it on Crunchyroll? Was it already translated (by fans or officially)?
Also, check if the manga is being pirated. It is a sad fact, but popular manga that will become anime is widely pirated, translated, fansubbed, etc.
Do some specialized Google searches for the manga series, its main characters and villains. Check the result count, and compare to other popular manga that already became anime.





After all of those factors, there are some things you can look for in specialized media to see if your favorite manga is really going to become anime:

Option: Did some studio or media company purchase the option for the IP? Options are commonplace in the Western media world, but it's becoming very popular around the world. Check the media and news for the option signing.

Rumors: Check some blogs (mostly in Japanese) for the titles they think will make next season (Dear Reader: suggest some blogs in the comments).

Wikipedia: The folks at the WikiProject Anime and Manga work really hard to keep their corner of the wiki fresh. If your manga series already have a Wikipedia page, chances are high.



As for your particular manga, I would say it certainly will become anime.