You were right from the first title. "行こうよ" Let's Go is the most literal and most likely the title for this song. It could also be "Let's Go Together" since "行こう" (Ikou) means Let's Go and "よ" (Yo) is used mostly to emphasize. I think when you could propose titles again.. it would likely be 行こうよ ft. 初音ミク(Hastune Miku) as its listed in vocalDB.
https://vocadb.net/S/436954
It seems likely abandoned the account as his last song was made in 2009.
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lawngreen
2342 days ago
tramute0
2342 days ago
tramute0
2342 days ago
lawngreen
2342 days ago