It was the day in WWII when the British forces in Singapore unconditionally surrendered to the Japanese army lead by General Tomoyuki Yamashita!!

Also it was the day in 1948 when the Department of Justice was abolished and the Ministry of Justice of established.

If we're talking about pre-WWII then it was day that USS Maine sank which triggered the Spanish–American War. It was also the day when Ferdinand III ascended the throne of Holy Roman Emperor.

Hey, Nenohi.

Oh, it's Nenohi.

SAVE ME!!

What day ("nan no hi") is February 15?

It's Nenohi!

I understand already, that's more than enough.

It's my bad ok?

You know what, Yukikaze?

She always responds "it's Nenohi's day". (her in game introduction line)

Let's tease her a little.

Er? You shouldn't do that, Shimakaze ~

MUHAHAHAHA!

Er?

A-Ah...

Was that so ~

This idiot always responds this way!!