As a foodie - I used to look down on Ketchup myself - but as I got older, I turned around.
There's something nostalgic about the flavor. Flavor of childhood.
I went to Kayashima restaurant in Musashino - (I think it appeared on J-drama Solitary Gourmet S1 or 2) when I visited Ghibli Museum in Japan a couple years back. This is Ketchup spaghetti - called Napolitan.
Yes, it's not Italian - and the spaghetti is very well over-cooked, but it's also very very comforting. It was little past Christmas and especially a chilly and rather windy day - a nice plate of this, served with Miso soup and a good chunk of side dish (unlike the picture here, I chose the ginger-pork, but you can also choose Shumai - lol)... peppered with hot Tabasco sauce + generic that green bottled Parmasan grated cheese - I thought I was back in 80s. The decor in the restaurant was straight up from 80s Showa time too. Food was great, price was very very reasonable (under 10 bucks, IIRC), which includes coffee or a drink.
Highly recommend the place if anyone fancy Showa style of nostalgia & quick lunch - it's only about 15-20 min walking distance from Ghibli Museum in Mitaka - thru a very nice park - and the shop is also near by a shopping district & the Chuo subway station into the city, which you would need to take it back to Tokyo.... IF you have any money left from visiting Ghibli Museum's souvenir shop that is.