In Japanese culture, attending a wedding is generally considered a significant social event, and it is expected that close friends and family members will attend if invited. Not attending a Japanese wedding, especially if you have a close relationship with the couple, could be perceived as rude or a lack of consideration for the couple's feelings.
However, there can be valid reasons for not attending a wedding, such as scheduling conflicts, financial constraints, or other personal obligations. In such cases, it's crucial to communicate your situation politely and in advance to the couple. Express your regret sincerely, and if possible, send a thoughtful gift or card to show your support and well-wishes.
If you cannot attend, offering a sincere explanation and showing your understanding of the importance of the occasion in Japanese culture will demonstrate respect and consideration for the couple's feelings.