Anime that is 25 episodes or less?

[Geno Rhapsody]

[Ja.Lo.Yo.Lo.Ti.]

If you like action/mafia type stuff, I recommend [91 Days] and [GANGSTA.].

Unfortunately, the studio who made GANGSTA. had to file for bankruptsy, so it is currently unknown if another studio will pick up the next season. They ended it at a good place, albeit a cliffhanger.  

[Psychedelic Gamer]

I'd recommend:

My Hero Academia (of course i'd put this first, 13 episodes and 1 for season 2 so far)
Amnesia (12)
Angel Beats (13)
Baccano! (16)

I know it surpasses your 25 limit but Cowboy Bebop is also good with it's 26 episodes, sorry I don't know much short anime  

[kane tsuku]

What do you think of SAO Alicization?  

[kane tsuku]

And Yakusoku no Neverland  

[kane tsuku]

And HINOMARUZUMOU  

[SuzuiChan]

Ill send these one by one so please dont mind me spamming
A-Channel
Tooru and Run have been best friends forever, so when Tooru learns that she's managed to get into the same high school as Run, she runs to tell her... only to find Run in a compromising position with yet another girl, Yuko. Needless to say, that makes things a bit awkward at school, with Tooru fending off those who might be interested in Run while Yuko and their other girlfriend, Nagi, have to deal with Run's own penchant for drama. (MyAnimelist)
 

[SuzuiChan]

A.I.C.O incarnation
Set in the near future in Japan, year 2035. A major incident was known as "Burst" which was caused by researching artificial life. A certain AI called "Matter" has eroded the Kurobe Gorge. Entering the research city, which has been called as humanity's last hope, has been prohibited by the government.

Two years later, Aiko Tachibana, a 15-year-old girl who lost her family from the incident, was told by a transfer student named Yuuya Kanzaki the truth that Aiko didn't know regarding a secret hidden within her body. The key to solve the mystery is said to be in the Primary Point, the center of Burst. When a boy and a girl, who bears the future of humanity, meet, what will be the new truth? (MyAnimelist)
 

[SuzuiChan]

Anne Happy
Tennomifune Academy is an elite institution for the best and the brightest, with the exception of Class 1-7, the so-called "Happiness Class." Each member of the classroom copes with personal misfortunes, and the special class is geared to help them move past their issues and find true happiness.

After being accepted into the academy, An Hanakoizumi, Ruri Hibarigaoka, and Botan Kumegawa find themselves placed into the Happiness Class, plagued by dreadful luck, love problems, and bad health respectively. Alongside their classmates, they do their best to overcome the difficulties they are faced with in pursuit of a life filled with joy.
 

[SuzuiChan]

Ao no exorcist
Humans and demons are two sides of the same coin, as are Assiah and Gehenna, their respective worlds. The only way to travel between the realms is by the means of possession, like in ghost stories. However, Satan, the ruler of Gehenna, cannot find a suitable host to possess and therefore, remains imprisoned in his world. In a desperate attempt to conquer Assiah, he sends his son instead, intending for him to eventually grow into a vessel capable of possession by the demon king.

Ao no Exorcist follows Rin Okumura who appears to be an ordinary, somewhat troublesome teenager—that is until one day he is ambushed by demons. His world turns upside down when he discovers that he is in fact the very son of Satan and that his demon father wishes for him to return so they can conquer Assiah together. Not wanting to join the king of Gehenna, Rin decides to begin training to become an exorcist so that he can fight to defend Assiah alongside his brother Yukio. (MyAnimelist)
 

[SuzuiChan]

Banana Fish
Aslan Jade Callenreese, known as Ash Lynx, was a runaway picked off the streets of New York City and raised by the infamous godfather of the mafia, Dino Golzine. Now 17 years old and the boss of his own gang, Ash gets his hands on a mysterious drug called "Banana Fish"—the same two words his older brother, Griffin, has muttered since his return from the Iraq War. However, his investigation is hindered when Dino sends his men to retrieve the drug from Ash at an underground bar he uses as a hideout.

At the bar, Skip, Ash's friend, introduces him to Shunichi Ibe and his assistant, Eiji Okumura, who are Japanese photographers reporting on American street gangs. However, their conversation is interrupted when Shorter Wong, one of Ash's allies, calls to warn him about Dino. Soon, Dino's men storm the bar, and in the ensuing chaos kidnap Skip and Eiji. Now, Ash must find a way to rescue them and continue his investigation into Banana Fish, but will his history with the mafia prevent him from succeeding?(MyAnimelist)