Keishichou Tokumubu Tokushu Kyouakuhan Taisakushitsu Dainanaka: Tokunana OVA  

Special Crime Investigation Unit - Special 7 OVA, Special Crime Investigation Unit - Special 7 Episode 0.5, 警視庁 特務部 特殊凶悪犯対策室 第七課 -トクナナ- OVA File.0.5「一年前、二条クジャクの憂い」, Special 7: Special Crime Investigation Unit - One Year Earlier: Kujaku Nijo's Melancholy, Keishicho Tokumu-bu Tokushu Kyoaku-han Taisaku-Shitsu Dai-Nana-ka: Tokunana OVA File 0.5, Special Crime Investigation Unit - Special 7 Episode OVA

What is the main focus of the OVA? It takes place one year before the start of the anime series, specifically during Kujaku Nijou's entry into the group.