Integral OB, etc. tank systems sometimes need a 'boost' to completely fill the carburetor and to get the carb float to its proper (spec) level - needed to have the correct air/fuel ratio.
As a trial, open the 'gas cap', seal the tank opening with your mouth and BLOW (5 - 10 seconds) into the tank to pressurize the fuel ... will fill the carb bowl until the float valve closes. If this corrects the hard-start, then either get or retrofit an external tank with 'squeeze bulb' or install a mini-squeeze bulb (Walbro, etc.) between the tank and the carb.
On small HP OBs BE SURE to only use FRESH (less than 30-45 day old) gasoline, dont depend on 'stabilizers but still use them, and BE SURE to always run the engine DRY of fuel when shutting down. For storage of more than a month or two, always open the carb drain plug to BE SURE that no gasoline is remaining in the carb bowl ... you can squirt in Isopropyl alcohol (IPA) to help keep the developed 'varnish and gums' to a minimum.
The correct starting fuel/air ratio for most Tohatsu (6hp) OB will be with the throttle set EXACTLY with the indicator between the 'rabbit' and the 'turtle' and the choke pulled - 'all the way out'. If you need to start on either side of that 'index' then the carb usually need cleaning and readjustment.
The usage of 'ethanol free' marine fuels (not available everywhere) will greatly help with 'hard-starting' and degraded performance. Go to ValvTect website to locate 'ethanol free marine fuels'. Locator: ValvTect - Certified Marinas
Good luck, but expect such nonsense to get much worse with increasing ethanol content in gasoline.