Good morning, NBC News readers.

Japan's Emperor Akihito abdicated this morning, President Donald Trump has sued two banks to block congressional investigations, and a Somali-American woman is breaking down barriers in a burkini.

Here's what else we're watching.

Trump sues to block banks from giving financial records to Congress

The president has moved to thwart ongoing House investigations into him.

Trump and several members of his family sued Deutsche Bank and Capital One on Monday, seeking to prevent them from responding to congressional subpoenas for information about the president's finances.

The House Intelligence and Financial Services committees issued the subpoenas to several banks as part of their investigations of alleged foreign influence on U.S. elections.

The suit filed in U.S. District Court in Manhattan says the subpoenas "have no legitimate or lawful purpose," and alleges they were issued "to ferret about for any material that might be used to cause him political damage."

Extremists celebrated online as synagogue shooting unfolded

As a gunman killed one person and wounded three others at a synagogue near San Diego on Saturday, white supremacists descended on a Facebook page connected to the suspected shooter to express support and push racist propaganda.

The shooting adds to a growing list of violent acts with ties to fringe parts of the internet that can also be found on mainstream platforms — particularly Facebook.

“At this point, given all we know about how extremists organize across platforms, there’s no excuse for Facebook,” said Melissa Ryan, an extremism researcher at Hope Not Hate, an advocacy group that tries to counter racism.

'I am a union man': Biden stakes ground at first campaign event

Former Vice President Joe Biden made his first official appearance as a 2020 presidential candidate Monday, taking on President Donald Trump at a campaign rally and imploring Americans to rebuild the middle class.

The former vice president made no reference to the other Democratic candidates and stuck largely to familiar issues.

"The major moral obligation of our time is to restore, rebuild and respect the backbone of America — the middle class," he said.

'Boyz n the Hood' director John Singleton dies at 51

At 24, Singleton became the youngest and the first black filmmaker to receive an Oscar nomination for best director and best original screenplay for "Boyz n the Hood."

He died Monday due to complications from a stroke he suffered almost two weeks ago.

Tributes to the filmmaker poured in on social media as reports of the filmmaker's fading health began to surface.

"John was a brave artist and a true inspiration. His vision changed everything," wrote Oscar-winner Jordan Peel.

End of an era for the Chrysanthemum Throne

Emperor Akihito abdicated Japan's throne Tuesday, becoming the country's first to do so in more than two centuries.

He leaves behind an imposing legacy for his eldest son, Crown Prince Naruhito, 59, who will succeed him.

“I would say that he is a revolutionary emperor compared to all of the emperors in the past,” said one Japanese journalist who is an expert on the imperial system.

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Plus

Give me your tired, your poor — and a check. Trump has proposed charging asylum-seekers a fee to process their applications.

Thanks for the "courtesy and humor": Deputy Attorney General Rod Rosenstein submitted his resignation to Trump and will be leaving the Justice Department May 11.

The NRA's Wayne LaPierre won re-election as the gun lobby's CEO despite internal struggles.

"I am proud to be a gay son of God": A Brigham Young University student came out during his valedictorian speech.

Pope Francis offered a warning to hair stylists: Thou shalt not gossip.

THINK about it

Dr. Google is making real doctors' jobs harder and putting patients at risk, physician Jalal Baig writes in an opinion piece.

Science + Tech = MACH

The moon may have formed after a giant Mars-sized rock hit a magma-covered newborn Earth, a new study finds.

Live BETTER

On a budget? Here's how you can actually save money by going green.

One fun thing

Somali-American model Halima Aden has made Sports Illustrated history by becoming the first woman to wear a burkini and a hijab for the 2019 swimsuit edition.

For Aden, 21, who was born in Kenya and moved to Minnesota as a child, the photo shoot at Watamu Beach in Kenya was "literally a dream come true."

“I keep thinking to 6-year-old me who, in this same country, was in a refugee camp,” she said during her shoot. “So to grow up to live the American dream, to come back to Kenya and shoot for SI in the most beautiful parts of Kenya — I don’t think that’s a story that anybody could make up.”

“We believe beauty knows no boundaries,” Sports Illustrated Swimsuit editor MJ Day said. Yu Tsai / Sports Illustrated

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Thanks, Petra