Evermay Estate in Georgetown. (Stu Estler)

What on earth will Ryuji Ueno and Sachiko Kuno do with two of Georgetown’s most expensive homes?

The quiet biotech entrepreneurs, who made an unexpected splash last year as the region’s premier mansion-collectors, haven’t spoken publicly about their plans. But we now know they plan to both live (at least part-time) in the more expensive of the two — the $22 million Evermay estate — and base their charitable foundation there.

The couple, said to be historic-preservation fanatics, also bought the nearby Halcyon House last year for $11 million, augmenting a mini-empire that includes three big homes n Potomac, two on the Eastern Shore and another rowhouse in Georgetown. (** Meet Ryuji Ueno and Sachiko Kuno **)

In an application filed with the District’s Board of Zoning Adjustment, the Japanese-born married scientists are seeking a “special exception” to set up a non-profit at the 210-year-old Evermay, which sits on 3 1 / 2 acres overlooking Rock Creek Park and the Washington Monument.

Ueno and Kuno will “maintain dwelling quarters” at the 10,000-square-foot home, according to the filing — but the more ambitious plans are centered on their S&R Foundation. Originally set up to support medical researchers and young artists in the U.S. and Japan, the group is now branching out to aid response to catastrophes like last year’s hurricanes and tsunamis, the application says. At Evermay, they would run the foundation’s business and host several meetings, concerts and dinners a year.

But not too many, and not too big, the foundation promises: mindful, it seems, of neighborhood tensions over Evermay’s recent past as a popular wedding venue. The estate will not be rented out for special events, the foundation said. Most of its private affairs will be held during business hours and for fewer than 50 people, who can park on the estate instead of the street. (The Old Georgetown Board already has given approval for a new one-story garage on the property.)

The application will get a hearing Feb. 28. Mary Carolyn Brown, an attorney for Ueno and Kuno, said they’re pleased with its progress thus far. “We’re very fortunate to have the support of the immediate neighbors.”

Inside Halcyon House, Ueno’s and Kuno’s other magnificent mansion. (Bob Narod)

As for Halcyon House — well, one mansion at a time, okay? No word thus far on their plans for 1787 home on Prospect Street, and nothing on file with city zoning officials.

Read also: Curbed DC on Evermay

Read earlier: Halcyon, Evermay buyers want to preserve historic homes (photos), 11/22/11

Halcyon House buyers: Ueno and Kuno, also bought Georgetown’s Evermay, 11/21/11

A family’s hidden history is revealed after sale of their grand Georgetown estate, 10/15/11

Georgetown mansion Evermay purchased by biotech entrepreneurs, 7/25/11

Historic Evermay estate: $49 million. In this economy?, 10/4/08

Centuries of Drama at Halcyon House, 8/30/08