Arina is one of the youngest member of Yua's team beside Miu. But there's something different about Arina. Her cold and straightforward personality is not common for a girl her age. It feels like she's already been through a lot.
Walkthrough:
Make sure you have already promoted Yua and let Yua lead her own team as a VP
Make sure you have already slept with Yua, Miu and Minami
She's new to the job, check on her work often. She will tell you how uneasy for her to work alongside Eva's team
Go to the office lobby at before 8pm, Eva will meet you and give you information regarding Yua's team suspicious activity
After office hour (6pm) ask Arina to go for a drink just the two of us. Try to get as much information from her. Ask her about credit approval and financial transaction data.
In the next day (7 - 12PM) ask her again about the data. She will subtly refuse and kiss you instead
Fool around with her for few times (5-7times). And when you're making out in the car, if you have already fooled around with her for few times, you can agree to her terms: Not to ask about financial data anymore, and she will let you do her as much as you want
You can call her to come to your apartment in the weekend (compact/studio apartment you rent for your rendezvous with Aoi).
Havefun with her for few times 5-7x
Go to the office lobby before 8pm, Yua will call you about the transaction data you kept asking on Arina
Enjoy Yua-Minami-Arina scene (all of the scenes are repeatable). To repeat the foursome scene, go to your medium apartment at night, make sure Yua already live there, and when at night in your bedroom where Yua already waited for you, you can ask her to call Minami and Arina to join the fun
Yua isn’t calinng