Natsu no Nikki (Summer Diary) (夏の日記 (Summer Diary); or simply Summer Diary) is the Japanese solo debut mini album by Lee Minhyuk. It was released on July 25, 2018 with "Natsu no Nikki (Summer Diary)" serving as the album's title track.
The physical release comes in two editions: a CD only edition (type A) and a CD+DVD+Mini Photobook (type B). Each editions also include a randomly selected trading card among four.
- "Stay" - 3:27
- "Natsu no Nikki (夏の日記) (Summer Diary)" - 3:22
- "All Day" - 3:40
- "Otsukisama e (お月様へ) (Dear Moon)" - 4:08
- "About Time (Solo Ver.)" - 3:47
- DVD (Type B only)
- "Natsu no Nikki (夏の日記) (Summer Diary)" music video