It's hard to tell if this is good for a yandere tag... Since Ushio got desperate and decided that locking him would be the only option.
I'd say Misery-style locking up your love interest so no one else can have him is close enough to yandere. It's still a case of insane/obsessive behavior motivated by insecurity and desire.
Hiyaa!I want to be with you forever, Admiral... I'm sorry... I'm sorry...P-Please, don't worry about me...I-I'm so sorry... But if I don't do this, other girls will take you away...Why do you worry about me so much? Maybe, by any chance, you like me, Admiral...? If this is the case, then I'm happy, but the other girls are also cute, they'll quickly take you away from me. It's natural for someone like me, but still it's hard... Ugh...