It's Zhan Zheng Xi.
...and not Zhan Zheng Xi Xixi.
Chinese naming conventions
They are such that the first word in the name is the surname, which is different from "English" names where the surname comes after the name.
Essentially, the first word in this character's name is: 'Zhan'. This would be the surname, also known as 姓 (xìng).
I have found the original webcomic in Chinese: https://ac.qq.com/Comic/comicInfo/id/630166
Meaning Of "What if..."
I have taken a look at the webcomic in Chinese. From my perspective, this webcomic seems to be filled with sexual innuendos. And it is no surprise that the Tumblr website has "yaoi" in the URL. Wikipedia writes:
Yaoi, also known as boys' ...
The following Latinized transcriptions - Zhan Zhengxi, Zhan Zheng Xi, and Zhan Xixi - are all Latin-based, specifically Pinyin-based, transcriptions of the original Chinese characters.
The Zhan surname may refer to: 展, 湛, 詹, 占, or 战/戰. They are all converted into Zhan in Pinyin. Without reading the original Chinese, it is impossible to know which logogram ...