My first "original" comic was super guilty of that too
I wrote it back in middle school after only having done pure fan comics before. It actually started out as a fan comic of the manga "+Anima" as well, before I decided that I wanted to do an original story instead. Even so, it ended up just being a frankenstein monster of borrowed elements from just about everything else I liked at the time.
The isekai elements (before I knew that was a whole genre) were borrowed from series like MAR and Dragon Drive,
The charm system was kind of a mix between MAR's arms and Megaman Battle Network's battle chips,
the magic system was almost completely ripped from Zatch Bell,
the animal transformation portion of the magic was carried over from +Anima,
the main character's name and general hairstyle was grabbed from the game Rune Factory,
the main char's best friend is one of my friend's OCs that he let me borrow,
Several other main characters were stolen from a forum roleplay I made for my story on the Gaia Online forums back in the day, which were all technically other people's OCs...
etc. etc.
When smashed together I think it did actually come together to something relatively original, but it was still just so much idea theft xD
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My current comic is straightforward: it started out as a D&D campaign last year~ It's a retelling/adaptation
It's been an interesting project consequentially because I only had direct control over one of the characters, the other 4 party members all had other players acting for them, of course, and the overall plot and events were dictated by the DM. So in a way it's almost like a collaborative storytelling effort xD