Of all the legacy Naruto characters to play a role in Boruto: Naruto Next Generations, the one with the most untapped potential remains Anko Mitarashi. Anko started life as one of the proctors of the Chunin Exam, before evolving into a complex character with a complicated history with then-main antagonist Orochimaru.
On paper, her transition into the 43-year-old woman we see in Boruto is honestly a pretty clever and interesting way to write her. She's taken on the role of teacher, in a very different place in life while still having some immature aspects to her personality. However, rather than use this set-up to explore a character with some intense past trauma growing up, she becomes the butt-end of jokes and almost irrelevant to the greater plot. Fans of Anko can't help but feel the character was done dirty by not being given any real role in the plot.
Anko's Flattened Personality Neutralizes Any Attempt at Developing Her
In the original series, Anko had a lot of development and trauma that could have been fascinating to explore going into Boruto. She was older than Naruto but had a similar immaturity level. She idolized Orochimaru as a young girl but was used and manipulated by him. She's constantly defined by her relationship to the villain, both due to how much he taught her and how he placed the Cursed Seal of Heaven seal on her neck, being the only one to survive the process. He ultimately revives himself through the curse he placed on her, and she ultimately feels responsible for all the crimes he committed.
Anko's arc in Boruto seemed to open the door to her continued growth, showing her in a more mature role and a position where she can help raise the next generation of ninja. Because of this, you'd think she would have a relationship with the new characters or offer insightful advice. However, outside of the Graduation Exams Arc, she's irrelevant to the greater plot. She has some scenes here and there, but none of them are important, and she takes very little action on her own that progresses the narrative.
To make matters more complicated, Orochimaru now has a son, Mitsuki. There's so much potential for Anko and Mitsuki to have a complicated, nuanced relationship due to their ties to Orochimaru, but this is never explored. It's somewhat problematic that Orochimaru, a villain who made Anko's life miserable, plays a more constructive role in Boruto's plot than one of the many people whose lives were derailed by him.
Anko's Character Has Becomes a Fat Joke
The fact that Anko got heavier in Boruto isn't a bad thing. What is bad are the constant fat jokes and stereotypes she's subjected to. In Boruto, Anko is presented as lazy and a food-addict. People constantly make comments about her body or her inability to find a husband. She's treated like a failure, despite being an incredibly powerful character who helped save the entire ninja world on more than one occasion.
These jokes could have been counter-balanced by her taking an active part in the greater narrative, even as a distant adult. However, she doesn't. The only fat stereotype Anko doesn't fall into is constantly dieting or worrying about her weight, which, while a nice change of pace, doesn't change how problematic her portrayal otherwise is.
Compare Anko's characterization in Boruto which that of My Hero Academia's plus size heroes, Fat Gum and Inku Midoriya. Both are heavy-set characters, but they're given non-stereotypical personalities, compelling character arcs and, in the powerful Fat Gum's cases, chances to get involved in the action. This comparison makes clear that Anko's role in the narrative is to serve as a walking joke, with only a couple of scenes here and there to remind the audience that, yes, she is one of the most powerful ninja around. One can't help but feel that she was done dirty.