This is a replacement cylinder for the V-18 MX(4350). You should be able to replace it yourself, as there are many replacement videos available online, even for beginners. It uses a temple key, so it offers higher security than standard keys. It was used for about six months and is being sold because it's no longer needed after a door renovation. There are three keys. Two are in good condition, but one shows signs of use. (The key tips are blurred in the photos for security reasons.) A new one currently costs over 10,000 yen on Amazon, so how about this more affordable option?