Stamp price for letter

Hi all! I would like to know what's the price for the stamp from Osaka Japan to China, and also to Malaysia? I'm following a tour and it's hard for me to get to the post office myself and the counter guy from 7-11 doesn't know how much they cost. Thank you SO MUCH! x

From Japan to China and Malaysia, via air mail, a letter (envelope size of 14 - 23.5cm by 9 - 12cm) up to 25g is 90 yen, up to 50g is 160 yen. Regular sized postcards will be 70 yen to any country around the world.

Rate is different by air or surface(ship) mail.
Read all.
https://www.post.japanpost.jp/int/index_en.html
https://www.post.japanpost.jp/int/service/letter_en.html
https://www.post.japanpost.jp/cgi-charge/index.php?lang=_en
https://www.post.japanpost.jp/int/use/index_en.html
https://www.post.japanpost.jp/int/question/index_en.html

In Japan "Japan Post(company name in ENG)" only.
No other mail service network company for personal custmer.
(except for compamy business mails/documents delivery)

Some major terminal large post office window open 24h like convenience store.
http://i.imgsafe.org/917b6bb.jpg
Calling "Post office" is "yuubin-kyoku(郵便局)" in JP.
Ask Hotel/tour staff or local people.

Convenience store cannot accept mail delivery
but only sales regular stamps mostly no different as rate validity.
(no sales special desgin one as a sheet/5-10 stamps set)
https://kitte-shop.post.japanpost.jp/goods/item_list.asp?tag_id=ko01&s...
https://www.post.japanpost.jp/kitte_hagaki/stamp/new/index.html?seturl...
Say "---YEN bun no kitte wo kudasai or onegai-simasu." at register counter.
(kitte/切手 means stamp, kudasai or onegai-simasu means "pls")

Convenience store cannot accept mail delivery

That's not true, a lot of convenience stores have mailboxes inside the store.

a lot of convenience stores have mailboxes inside the store.

That's great to know, because in the 40 something years of living in Japan I'd never noticed one. The internet tells me that a lot of Lawson stores have them.

Well, convenience stores don't have "postal service counter" where they will take care of postal services (such as weighing envelopes/parcels and telling you how much postage will be), but if you tell them you want stamps for XXX yen, they should be able to sell you, and yes there are red mailboxes available at many Lawsons. You might not really notice them because often they are attached to the side of the counter, but I've seen some :)