The 28-year-old died from heatstroke on Sunday at Hirakata Park after dancing for 20 minutes while wearing a 16kg costume.
In response, the park has cancelled all mascot events this summer.
Official figures revealed more than 5,000 people sought hospital treatment due to the heatwave in the last week.
According to Kyodo news agency, more than 50% of those hospitalised were aged 65 and over.
Temperatures are expected to remain higher than average for the next week.
The mascot fell ill as he performed at around 19.30 (10:30 GMT) on 28 July, the Asahi Shimbun reported. Half an hour later, the temperature in the city was 28.7 degrees, the newspaper added.
He lost consciousness and was rushed to hospital where he died.
In a statement, owners of the park, Keihan Leisure Service promised to "find the cause" of the incident and "work to prevent it from happening again", the Japan Times said.
It's not the first time Japan has been gripped by a deadly heatwave. In July last year, the country's weather agency declared a heatwave a natural disasterafter 65 people died from heat related deaths within one week.
BBC
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