The themes could include the journey of them coming to terms with their feelings for each other. Also, the idea of Ging's past and how it affects their relationship with Gon could be a major theme. There might also be themes about how their relationship impacts the world around them in the Hunter x Hunter universe.
I'm not sure specifically which Ging meets Gon in a 'boyfriend' context fanfictions are out there. You could try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net. Just type in relevant keywords and browse through the results.
I don't have enough information. Maybe the attack is a major turning point, or it could be a minor event that sets up future events. The nature of the attack and its significance would vary depending on how the manga's story unfolds.
The cartoon moon on Christmas Eve can have several meanings. Maybe it represents a peaceful and enchanting night, or it could be a way to make the holiday more visually appealing and unique for kids.
Well, usually in cartoons, a transparent magnifying glass might be shown as having a clear, shiny surface that makes it easy to see through. It could also be drawn with some cute or unique designs to make it more appealing.