Jii Tousaku
Japanese title: 自慰倒錯
Alternative titles: Jii Tousaku: Koukishin, Jii Tousaku Koukishin, Jii Tousaku II: Hametsu e no Kairaku, Jii Tousaku II ~Hamestu e no Kairaku~
Type: OVA
Source: Visual novel
Episodes: 2
Status: Finished Airing
Aired: Aug 2, 2002 to Apr 16, 2004
Duration: 28 min per ep
Rating: Rx - Hentai
Studios: Rikuentai
Producers: Japan Home Video
Genres: Hentai

Based on the game by TinkerBell. 

Saeko is introduced to an online sex shop by her co-worker, Sayaka. Curiosity gets the best of her and she orders herself a small vibrator. After discovering the pleasures the sex toys bring her, she gets addicted to masturbation and finds herself doing it all the time. Soon enough, Sayaka joins her in her sex escapades and things start to escalate to new heights. 

(Source: AniDB)