Ｋ♥
Source: https://twitter.com/Strangestone/status/1198775181503655936

俺のこの手が真っ赤に燃える
Source: https://twitter.com/Strangestone/status/1198775484521172992

勝利を掴めと以下省略！
Source: https://twitter.com/Strangestone/status/1198775815099437059

今週はキング・オブ・ハート
Source: https://twitter.com/Strangestone/status/1198798460608225280

"Concentration" as in the pair-matching card game. The literal meaning "nervous breakdown" also applies to Onii-san's reaction in the last panel.

Ｋ♥
This is a reference to King of Heart from [i]Mobile Suit G Gundam[/i].
Source: https://twitter.com/Strangestone/status/1198775181503655936

This hand of mine is burning red!
Source: https://twitter.com/Strangestone/status/1198775484521172992

(Its loud roar tells me to) grasp victory! (Abbreviating the lengthy spiel.)
Source: https://twitter.com/Strangestone/status/1198775815099437059

This week's theme is "King of Heart".
Source: https://twitter.com/Strangestone/status/1198798460608225280