Furin Kazan

There head wear, and clothes look very Song dynasty Chinese

Correction. Not Iwo Jima island itself but the Ogasawara islands. And you got it!

Yes. Under that same unit there is a Lt Kudo. That's why I was wondering if it's from Iwo Jima because that unit participated in the defense. See the attached picture: 独立歩兵第３０５大隊 工藤文雄大尉 Same parent unit but different location on the island. Here Kudo is a 大尉 instead of 中尉. But if we're lucky enough here is could totally be them lol. Because a lot of these smaller units were formed hastily on the spot. It's totally possible that Lt Kudo used to serve under Colonel Sakata but was given command of a new independent unit. Also the Katakana says "Smith VM", initial of that Marine. Still, chances of us coincidentally identifying the owner of this pistol after a quick google search is still pretty low haha but something to hold on to I guess

Does it happen to be brought back from iwo jima?

That appears to be his surename 工藤 again. The kanji 藤 is just written in a simplified form this time. And often times the name of the unit is taken after it's commander. Does the bring back paperwork provide any more detail?

That's gotta be hard to pinpoint who he was. I bet there were many Sakata Butai's

坂田部隊 (Sakata Butai, Sakata Unit)　工藤中尉 (Kudo Chui)

The cursive stuff is beyond me lol. One one side the red stencil says 神田服部刀剣店謹製＝ Kanda Hattori Sword Store Made. Other side 七六二号= number 762, 佐野様=Sano Sama (Mr. Sano), what follows might be an address but don't quote me

家次-Ietsugu, ニツ胴- two bodies, 切手　恒川興左衛門-cutter, Tsunegawa Kousaemon, 桶居土壇入- Okeiyama (guessing location) 土壇 is how the bodies were mounted 天明四甲辰九月廾七日-Tenmei fourth year (1784) ninth month twenty-seventh day ps not an expert so might be wrong on certain things

豫州/松山-Yoshu/Matsuyama, 豫州 (or 予州) is another name for 伊予国 (Isu no kuni) , current day Ehime Prefecture. Yuzhou, which is written the same way, is an old Chinese geopolitical province dating back to the Han dynasty and subsequently Songshan (same kanjis as Matsuyama in Japanese) is another Chinese city/mountain in the Yunnan province. Very cool stuff

If I may, what's the complete date next to it?

Could it be the Someya School, who were kinko artists that drew heavy inspirations from Tani Buncho? And the name Someya also has the kanji 谷(Tani) in it (might be a little far fetched haha) Reference: https://books.google.com/books?id=OPfhAwAAQBAJ&pg=PA224&lpg=PA224&dq=%E8%B0%B7+tsuba+mei&source=bl&ots=_mQATN9Z0g&sig=ACfU3U1375k23TW8TH0GCW1SJVu4k-g2dg&hl=en&sa=X&ved=2ahUKEwiohfKM1K7pAhXUKs0KHaGfDmYQ6AEwBHoECAsQAQ#v=onepage&q&f=false (page 224)

Fake Yasukuni-to? Just for kicks the Kanji reads "Yasukuni tame wahei" I think they are trying to say "sacrifice for ones country for peace" but doesn't make sense to use the word yasukuni in this sense

“螳臂挡车” in Chinese "蟷螂の斧" in Japanese.. very famous proverb

Did a little research as I also find this interesting. There is a Showa Seki swordsmith (Seki Kaji Tosho) using the name 忠行 (Tadayuki) and his real name appears to be 河村 一三 (Kawamura Ichizo, out of Gifu) The following information is taken directly from japaneseswordindex.com "During WWII, more than 200 swordsmiths worked only at Seki province to supply qualified swords for their soldiers. Their names began to appear in Seki Tanrensho Booklet printed in 1939. Several smiths in this list worked as Rikugun Jumei Tosho (e.g. Nakata Kanehide) and produced both good and poor blades together. However, most of these seki smiths produced low grade Showato and should not be regarded as a Gendaito." Dos that match what you found as well?