The most advanced form of internet that is widely available in Japan is so called “optical fiber” or hikari / 光. The most easy provider to deal with that offers a minimum connection is FLET'S. The highest speed option is FLET's 光 Cross.

Most internet service providers simply provide an Internet connection on FLET's. For example, Sakura Mobile, AsahiNet, etc.

FLET's Hikari Cross requires 光配線方式, not VDSL/LAN. equipment.

See: https://business.ntt-east.co.jp/service/zenko/notice.html.

The preferred type is “フレッツ 光ネクスト ギガマンション・スマートタイプ 全戸加入プラン”.

ギガマンション・スマートタイプ導入物件は、ご希望に合わせて、入居者さまから個別にオプション料金をお支払いいただくことで、通信速度最大概ね10Gbps

https://business.ntt-east.co.jp/service/zenko/#anc_internet

This type is required: フレッツ光 全戸加入プランの物件