回答
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Yusaku Maezawa is the first Japanese private individual that arrived at the International Space Station for a 12-day stay.
"前澤友作さんが日本の民間人で初めてISSに滞在"
確か12日間の滞在予定でしたよね？
ISSに着いた最初の日本の民間人
the first Japanese private individual that arrived at the International Space Station
thatは関係代名詞
for a 12-day stay 12日間滞在
Yusaku Maezawa is the first Japanese private individual that arrived at the International Space Station for a 12-day stay.
日本 
