It's hard to give an exact time as it depends on the manga's plot development. But typically, Yuta Okkotsu shows up when certain events and character arcs lead to his introduction.
Expansion usually referred to the expansion, expansion, or extension of the original text to enrich the content of the text, increase the length of the story, expand the plot, and so on. In novel writing, expansion was a common literary technique that could make the story more lively and interesting, allowing the readers to understand the plot more deeply. Expansion could be achieved by adding details, changing the plot order, adding characters, and so on.
Not all Diablo 2 versions had expansion characters and non-expansion characters. There were many versions of Diablo 2 that had different storylines and character settings. Some versions included an expansion pack that introduced new characters and content, while others only included the traditional main story without an expansion pack. Therefore, not all Diablo 2 versions included expansion characters and non-expansion characters.