While there's no real way to make the concept of going back to an abusive girlfriend work, it might have been a little more palatable if the story had taken the time to show that Serina did, in fact, miss Kanon (apart from the crying after running away, which could be interpreted any number of ways), such as by showing her talking with "Aoi" about Kanon and actually talking about happier times. As it stands now, Kanon's just the woman who threw the remote control at her girlfriend for no reason, and nothing in the story helps with that extremely negative first impression.
We did get a number of her convos with "Aoi" translated, which are exactly about that - showing that Serina still cared about Kanon.
Most of the social media posts that show that Serina still cared were shown after the reunion.
https://dynasty-scans.com/chapters/to_meet_you_again#9
Before that, there's the slightly vague "I want to meet her" post on this page.
https://dynasty-scans.com/chapters/to_meet_you_again#4
My point is that it might have been nice to put a little more effort into building up how Serina feels about Kanon and perhaps show more redeeming elements to Kanon.
In response to KawaiiSuka, that's a realistic way to look at it, but the ending seems to be framed as a happy ending, with her overriding any concerns she has.
"I can't believe it. What are you, crazy?"- "She went that far because she loves me." Serina's refusing to doubt Kanon.
"I'm scared"- "I'm happy. She's precious." She doesn't care about her worries, only about how she feels in the moment.
"I'll just get screwed again"- "This time I'm sure it'll be okay" It's a bit of unwarranted optimism with regards to an abusive relationship.
"Even my friends told me to ditch her"- "What do the others know about us?" An abuse victim disregarding what others say and only caring about the abuser.