In the third and fourth part of a five-part interview with Masahiro Sakurai, we hear a bit more about Sakurai's interactions with Iwata overall. PushDustIn has translated the juicy tidbits, which you can find summarized below.
Sakurai says the first time he saw Iwata upset was back in the early days of HAL. The company was working on Metal Slader Glory, which took a number of years to develop, and almost bankrupted the company. Things were so dire that HAL was renting out apartments for work, and had to borrow a large sum of money to keep development going. This lead to Iwata being quite upset, but he was upset by the situation itself, and not the people involved.
Sakurai also recalls Iwata getting upset when he became president of Nintendo. There was a process of reorganization going on, and one meeting about technology lead to Iwata being upset with numerous responses from the team. It was these two instances that lead to Sakurai realizing how sincere a person Iwata was.
The second time that Sakurai saw Iwata upset was when he became the president of Nintendo. The company had to be reorganized, and there was a meeting dealing with technology. There wasn't really a response from the meeting which upset Iwata a little.
Finally, Sakurai shares a story about driving with Iwata to Narita Airport in Iwata's newly bought sports car. Iwata bought the car because he figured it was a 'now or never' kind of purchase, and if he didn't buy it he wouldn't be able to drive it.
In another section of the interview, Sakurai looks back on the days of working on Smash Bros. Brawl. You can find those details below.
Sakurai remembers telling Iwata that he was going to go freelance, which might lead to him working on non-Nintendo platforms. This news made Iwata a little sad, understandably. Sakurai actually had another project he wanted to work on at the time, but Iwata ended up wooing Sakurai back to work on Brawl.and Iwata Asks for Brawl.