Based on the relationship logic in the work, I'm starting to suspect that in the third episode, that... Katsuo's father's driver and bodyguard might actually be the blonde boy's father.
Firstly, in the official artbook, the man with glasses is noted as an "attendant," while the blonde boy is labeled as a "friend." (The blonde boy's reaction to sneaking away in the original work is also very interesting).
Secondly, comparing the appearances of these two in the original work: they have the same hair color + droopy eyes + dotted eyes + pale skin + face shape. It's very intriguing...
If this is indeed the case, it would be perfectly normal for the two to be familiar or even become friends.
Anyway, if this is true, his surname would be KUZNETSOV, and he's Russian. (Come to think of it, the driver fits my stereotype of a Russian bear quite well)

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作品の人間関係の論理に基づいて、3話のあの人...勝男の父親の運転手兼ボディーガードが実は金髪の少年の父親ではないかと疑い始めました。
まず、公式アートブックでは、眼鏡をかけた人物は「従者」と注釈があり、金髪の少年は「友人」となっています。（原作での金髪の少年の逃げ出す反応も興味深いです）。
次に、原作の二人の外見を比較すると：同じ髪の色＋垂れ目＋点目＋白い肌＋顔の形。非常に気になります...
もしそうだとすれば、二人が親しくなり、さらには友人になるのは極めて自然なことです。
とにかく、もしそうだとすれば、彼の姓KUZNETSOV、ロシア人ということになります。（そういえば、運転手はロシアの巨熊に対する私の固定観念にぴったりです）