Thanks for filing the issue!

Tried checking the issue on reported chrome version 70.0.3538.102 using Mac 10.14.1 with the below mentioned steps.
1. Launched Chrome
2. Navigated to https://www.soscisurvey.de/tools/view-chars.php
3. Cleared the input field.
4. Turned on Hiragana mode on Mac
5. Typed as per point no.3 in C#0
6. Clicked on 'Show me the characters' button.
It didn't show any characters. Attaching the screencast of the same for reference.

@Reporter: Could you please check the screencast and let us know if we have missed anything in the process. Any further inputs from your end may be helpful.

Deleted: 906032.mp4 810 KB

	906032.mp4 810 KB View Download

@vamshi.kommuri@chromium.org
Hi, thank you for checking the issue!

I can see that you clicked to choose あ from the input suggestion list.
Please note that clicking is not in the replication steps.

When I press the A key on my keyboard, it automatically shows あ.
You don't have to hold down Shift when you press A to make Chrome type the letter 'A', if that's what you did.
I'm sorry, it would have been more accurate if I had written 'Press' instead of 'Type' in the Step #3.
So Step #3 is PRESS the next keys in the following order.
A
Space
Tab
Delete
A
Delete
Delete


Also, here are my setting values if it's necessary to enable/disable certain options to replicate the issue.

Input modes:
Hiragana: Enabled
Full-width Romaji: Disabled
Katakata: Disabled
Half-width Katakana: Enabled
Romaji: Enabled

Caps Lock action: Caps Lock
Shift key action: Enter Romaji mode
Typing method: Romaji
Live Conversion: Disabled
Correct spelling: Disabled
Windows-live shortcuts: Disabled

Candidate window: 
Font: Hiragino Mincho ProN W6
Font size: 16
Predictive candidates: Enabled
Convert with punctuation: Disabled

Romaji layout: U.S
Punctuation: 。and 、
"/" key generates: ・ (Middle dot)
"¥" key generates: ¥（Yen sign）
Full-width numeral characters: Enabled

Speciality dictionaries: No entry

Hope it helps.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Hi, I just figured out that the issue was reproducible with Google Japanese IME and ATOK 2017 as well.
 
I also found a reduced replication steps.
The steps work for all the IMEs mentioned so far.

Steps:

1. Go to https://www.soscisurvey.de/tools/view-chars.php and clear the input box.
2. Turn on the Hiragana mode of a Japanese IME.
3. Press the following keys in the written order (Do nothing else in-between).

Space
A
Delete
Delete
Space
A
Delete
Delete

4. Click the 'Show me the characters' button.

Expected
No character should be in the text box.

Actual
It says U+3000 and 08 are in the text box.

As per comment #7, Able to reproduce the issue on reported chrome version 70.0.3538.102 also on latest chrome 72.0.3616.0 using Mac 10.14.0.  
 
Same behavior is seen on M60(60.0.3112.113) hence considering it as non-regression and marking it as Untriaged.

Thanks!

Mac triage: to lgrey@ for M73.