Bunga was the first to go.
It was just a few years after the Outlanders and Pridelanders united and Kovu and Kiara were married. The Guard all knew something was up when their youngest, and most immature member seemed to be growing up faster than the rest of them.
The brave-bordering-on-stupid honey badger had reached adulthood when Beshte was just reaching his mid teens and Kion's mane barely passed his chest. Though he matured significantly from when the Guard was first formed, Bunga never outgrew his catchphrase of "Zuka Zama!" Even as he grew older, he was always so full of life.
He never took a mate or had children- he much preferred the bachelor lifestyle, lounging around eating grubs, hanging with friends, and defending the Circle of Life.
Kion didn't take it very well. How do you cope with your best friend, who is the same age as you, dying of old age while you're just reaching adulthood? Simba passed away a few months after, peacefully in his sleep, and Nala a few days later, leaving Kiara and Kovu the sole rulers of Pride Rock.
A few years passed. Kiara gave birth to Kovu's cubs, a healthy, strong young prince who would one day become king, and a princess, whom Kion would train to be the next leader of the Lion Guard. Beshte watched as, one by one, his friends went on to have families of their own, while he was just barely reaching adulthood.
Under new leadership, the Pridelands changed drastically. It seemed that Kiara and Kovu had ushered in a Golden Age of the Pridelands, with a peace that hadn't been present since before Mufasa's reign. Reduced to Kion, Fuli, Beshte, and Ono, the Lion Guard didn't have much to do in those days. Janja's clan had since left the Outlands for some other place, so save for the occasional dispute between herds, or unwanted predator, the days passed by uneventfully.
Fuli was the next to pass away, though it was before her time. She died as she lived, defending her two young cubs from a sinister leopard who had wandered into the Pridelands.
Alerted to the fight by Ono, Kion and the royal family rushed to her aid, driving the leopard away. But it was too late, and the cheetah was already dead when they arrived. Her cubs were raised by the royal family, one going on to serve as a member of the next Lion Guard.
And then there was three.
Kion, Beshte, and Ono.
Though Beshte was still in his prime, the lion and egret were advancing into old age. First went Ono, peacefully in his sleep. Then went Kovu and Kiara, within days of each other. Kion lived about a year longer. He had never taken a mate or had cubs, but Beshte wouldn't let him die alone. He and Fuli's children were with him when he drew his last breath.
And for the first time in his life, Beshte was completely, utterly alone.
Many years passed. More than Beshte could count. He watched as his friend's children, and their children's children, were born, lived, and eventually died. He witnessed many kings and queens take their place in the Circle of Life, and many Lion Guards rise up to defend it.
He took a mate, had children, who grew up and had children of their own, and made friends with many different animals of varying lifespans, and Beshte's heart ached for them all. They were unaware how much longer they would live after their friends had died.
Beshte hadn't realized how long her would live after all his friends had died.
There came a day when he could no longer remember his friend's faces or voices.
There came a day when he was the only animal in the Pridelands that remembered their names.
He would have given anything, everything to have one more, precious day with his friends. Hear their voices, see their faces, laugh and play and defend the Pridelands, just like the old days.
But those days were long gone now, surviving only in the wisps of memory remaining in the old hippo's mind. Forty years had passed since Kion died, still more since Bunga and Fuli and Ono. Yet in many ways, it seemed that no time had passed at all since Kion had discovered the Roar of the Elders, and formed the Lion Guard.
Beshte held on to those memories for as long as he could, hoping and praying that one day, he would be reunited with his friends again.