* SoftBank plan gives Nikkei a hefty boost
* Dealers look to weak yen for gains through end-2016
By Ayai Tomisawa
TOKYO, Dec 7 (Reuters) - Japan's Nikkei share average rose on Wednesday morning after U.S. shares extended their gains, bouyed by index-heavyweight SoftBank after it announced a bold investment foray into U.S. businesses.
SoftBank rose as much as 5.1 percent after Chief Executive Masayoshi Son said he would invest $50 billion in U.S. companies.
The Nikkei gained 0.3 percent to 18,418.16 in midmorning trade. SoftBank contributed a hefty 31 points to the Nikkei, or more than a third of the benchmark index's point gains.
Nonetheless, traders said that because Japanese stocks had risen so sharply since the U.S. elections last month, profit-taking could kick in at any time.
"It looks hard to maintain this short-term rally," said Mitsushige Akino, a chief fund manager at Ichiyoshi Asset Management, adding that most of the big gains are coming from such index-heavy stocks such as Fast Retailing Co which rose 2.0 percent, as well as Softbank.
Financials and exporters were higher, with Mitsubishi UFJ Financial Group rising 1.7 percent, Mizuho Financial Group adding 1.6 percent, Toyota Motor Corp gaining 1.2 percent, Honda Motor Co adding 1.5 percent and Panasonic Corp up 2.8 percent.
Drug manufacturers were sold, with Takeda Pharmaceutical falling 0.8 percent and Eisai Co dropping 0.7 percent.
The dollar was steady at 113.990 yen after inching up about 0.2 percent overnight following a modest rise in U.S. bond yields.
Traders said that for the next few weeks through end-2016, hopes that Japanese exporters' earnings will be lifted by a weaker yen should support market sentiment.
"We see that the Nikkei testing its year highs toward the end of year is possible, as the market welcomes the current dollar-yen levels," said Takuya Takahashi, a strategist at Daiwa Securities.
The broader Topix gained 0.3 percent to 1,482.12 and the JPX-Nikkei Index 400 added 0.3 percent to 13,274.34. (Reporting by Ayai Tomisawa; Editing by Eric Meijer)